# On the Different Ways to Measure Production Speed | Christoph Roser

“There are many different ways to measure manufacturing speeds. Depending if you need the losses included or not, if you want parts per time or its inverse or only a time, single processes or entire systems, actual or current values, you may have a completely different number. This post will help you to sort out what is what…”

Sourced through Scoop.it from: www.allaboutlean.com

Michel Baudin‘s comments:

The main conclusion from this post is that, when discussing production speed, you should define your terms if you want to avoid confusion.

# Using Takt Time to Find Problems Earlier | Zsolt Fabók

See on Scoop.itlean manufacturing

“The idea of takt time comes from car manufacturing. It shows the elapsed time between two completely assembled cars leaving the factory floor. If the takt time is 2 hours, it means that the factory produces 12 cars a day (24h/2h = 12)…”

Michel Baudin‘s comments:

A nice effort from a software developer to discuss the relevance of the concept of takt to his profession, or lack thereof. Unfortunately, he gets a few details wrong.

The first sentence is “The idea of takt time comes from car manufacturing.” Well, not exactly. Try aircraft manufacturing in Germany in the 1930s.

His example of a car manufacturing plant making 12 cars/day is a bit odd. I suppose such plants may exist in the extreme luxury end of the industry, but 1,000 cars/day at a takt time of 1 minute while working two shifts/day is more common.

“Car manufacturers are producing the same kind of car over and over again.” Well, not exactly. In the past 100 years, the industry has changed. You now make multiple models of cars on the same line, and each unit has its own build manifest with configuration options.

And car companies do not change the takt time every week. It’s more like every four months. Contrary to what the author says, the takt time is not a tool for throughput prediction. The throughput prediction is an input to the calculation of the takt time,  which is a tool to drive how you design and operate production lines. It is adjusted to reflect changes in demand, but not fluctuations, because changing the takt time of a line involves rebalancing the jobs in it.

Having worked in both worlds, I agree that car manufacturing practices are irrelevant to software development. Software development is development, not production. If you want similarity and management tools with crossover value, you should look instead at product development in other industries, not the production of existing products.

See on zsoltfabok.com

# Lean is from Toyota, not Ford, and not 15th-century Venice boat builders

Anywhere but possibly inside Japan, finding local roots for Lean is useful to defuse nationalism when implementing it, but it is also risky. You start by giving a local pioneer credit  for what he actually did. Similarity of his insights with Lean then becomes enough to label him a “precursor.”  It may be a stretch, but it is a white lie, and it makes local engineers and managers so much more receptive! Further down this slippery slope, however, the local precursor becomes a “pioneer” and soon there is nothing to Lean beyond what he came up with, at which point his legacy impedes Lean  implementation more than it supports it. This is where Lean is attributed to Henry Ford.

In reality, while the founders of Toyota learned everything they could from foreign sources in early days, they and their successors are the ones who put the Toyota Production System (TPS) together and made it work, before the term “Lean Manufacturing” was coined. A Toyota alumnus told me that he never heard Toyota people claim they had invented anything; after all, they are in the car business, not the production system business. What is unique about their work is that they have integrated all the pieces — borrowed or not — into a system that outperformed the competition. As part of its 75th anniversary celebration, Toyota published the following illustration of its overall system:

From the Toyota 75th anniversary web site

They also published a detailed timeline of the development of TPS  from 1945 to 2005, highlighting the key challenges the company faced in each period, and the solutions it adopted in Just-In-Time and Jidoka. Each item has a short explanation in text, and is illustrated with cartoons, technical drawings, and photographs. It is an excellent and balanced account of the technical content of TPS, and I recommend going through it to understand how the pieces fit together.

Based on this timeline, other details contained in the 75th anniversary website, and a few other sources, I compiled the following summary, going back further in time, and emphasizing international exchanges. What I find most striking about this timeline is that the foreign inputs to TPS, primarily from the US and secondarily from Germany, were over by the mid 1950s, almost 60 years ago, and that, since the late 1970s, the flow is in the opposite direction, with the rest of world learning from Toyota.

TPS is still a work in progress. It has been and still is primarily an original development. The bulk of TPS has come from the minds of inventor Sakichi Toyoda, his son Kiichiro, engineers Taiichi Ohno and Shigeo Shingo, and hundreds of thousands of Toyota employees over decades. A trade secret until Toyota started training suppliers in the 1970s, TPS was revealed to the world with the publication of Taiichi Ohno’s book in 1978.

The American influence, particularly Ford’s, is readily acknowledged and played up in Toyota’s official literature. The German contribution, while not hidden, is in small print. Takt  is a central concept in TPS, and it came to Toyota from the Mitsubishi Aircraft plant in Nagoya, which had learned it from German aircraft manufacturer Junkers. After the subject of Takt came up in a LinkedIn forum a few months ago, I pulled on this linguistic thread to see what came out, and I was surprised by the magnitude of it, essentially a whole production system for aircraft, including some principles of supply chain management. It is summarized in the following blog posts:

Toyota’s study of automotive technology also included reverse engineering a 1936 DKW from Germany, and Toyota’s first postwar model, the 1947 SA, looked like a Volkswagen beetle.

Why Toyota designers chose to imitate this particular car at that particular time is another mystery, but not relevant to the key point here, which is that all of this borrowing from abroad is ancient history.

By Michel Baudin Posted in History

# Takt time – Transfer from Germany to Japan in World War II

In Americanization and its Limits, p. 325, the sentence “In February and March 1942, visiting engineers from the German firm Junkers lectured to Japanese aircraft engineers on high-volume manufacture of fuselages and engines.” made me wonder how, in the middle of the war, engineers just “visited” from Germany. It’s not as if you could then hop on a plane in Berlin and land a few hours later in Tokyo.

According to Wikipedia, until Germany invaded Russia in June, 1941, Japanese and Germans visited each other by riding the Transsiberian railway, from Moscow to Vladivostok, which took a few weeks. After that, the only way to travel was by blockade-running submarines, and only six such trips occurred, carrying in total 96 people from Germany to Japan, and 89 in the other direction.

According to the 1946 US Air Force report on the Japanese aircraft industry, passage of materials by rail stopped after Germany attacked Russia, but passage of personnel continued. This is surprising, and it is difficult to imagine how Germans could have allowed to travel that road, but Japan was not at war with Russia until August, 1945. It had a neutrality pact with the Soviet Union, which must have allowed Japanese citizens to travel to Moscow under diplomatic cover, and then on to Germany through a neutral country like Sweden or Turkey.

Ernst Udet visited Japan, its air force and its aircraft industry in 1939. Early in 1941,  the train was still available  and General Yamashita — future “tiger of Malaya” hanged as a war criminal in 1946 — spent several months in Berlin. He brought back 250 aircraft technicians, engineers, and flight instructors. Given the timing and arithmetic, there is no way the vast majority of these 250 could have returned to Germany before the war ended.

The people who visited Mitsubishi aircraft must have been from that group, and must have been available for more than a lecture. My guess is that they stuck around to help Mitsubishi implement their Taktsystem. These people’s direct knowledge of the Junkers system is also as of 1941, before forced labor.

The JMA (Japan Management Association) currently is a large consulting firm in Japan. Shigeo Shingo worked there, and it is also where Nakajima coined the term TPM. The JMA already existed during the war, and, after the war, was instrumental in propagating techniques from aircraft manufacturing to other industries.

According to the same source, “Even in the early 1960s, the Japanese market for cars remained small and assemblers wanted to produce a variety of cars. The companies preferred to accommodate many types of cars on a single line, and consequently emphasized the need to equalize the cycle times of all production processes. This was rather similar to the situation at aircraft companies during the war…”

By Michel Baudin Posted in History

# Takt time – Even more about origins in German aircraft manufacturing

Earlier this week, I ran into John Paxton’s 2008 paper called Myth vs. Reality: The Question of Mass Production in WW-II, in which he makes a convincing case that production methods were far more advanced in the US aircraft industry than in Germany or Japan. It is really not in doubt. The point in trying to understand the Junkers Taktsystem is simply as one of the sources of TPS. World War II German and Japanese engineers could design advanced planes, like the first jetfighter, the Messerschmitt 262 that you can see in the Smithsonian today, or the Mitsubishi Zero. But, in production, they could not come anywhere near the one-bomber-an-hour performance of Ford’s Willow Run plant.

Yesterday, I was able to go to the main library at Stanford University, where they have about one foot on one shelf in the basement with books on the German aircraft industry in World War II. including in particular Lutz Budrass’s work on the subject and Holger Lorenz‘s Kennzeichen Junkers. Budrass’s book is a forbidding 1,000 pages of small print with a few grainy pictures, long on armament policies and politics, but short on technology:

Lorenz’s book is much more accessible and contains many high-quality photographs, which contradict Paxton when he says:

“Photographs from the era show this  difference. Classic photos from Vickers and DeHavilland (British) and Junkers and Heinkel (German) production facilities show  isolated aircraft in ‘final assembly’, in  stationary jigs, being assembled by ‘work  gangs’, embodying the ‘craft production’  process. In contrast, photographs from  Grumman, North American, Republic, and others show rolling final assembly processes, with aircraft moving from station  to station, much like Model T assembly  twenty years earlier.”

What Paxton writes is not consistent with what little I have seen about  the Junkers Taktsystem, and it is not consistent with the photographic evidence either, which shows that, at Junkers, the final assembly methods in the 1930s were eerily similar to those today for airliners, as you can see in the following side-by-side comparison:

Junkers clearly had a rolling assembly line, albeit one that, unlike the Boeing 737 line, was not continuously moving, Otherwise, the similarities extend even to the kits of parts that are rolled over to each plane. Of course, this is Junkers, not the whole of the German aircraft industry at the time, but Junkers is the one we are interested in, because of their Taktsystem and their transfer of this method to Mitsubishi aircraft in Nagoya, through which it reached Toyota. Other companies used a variety of methods. As we can see on the following picture Heinkel 111 bombers appear to have been assembled on fixed stations in 1939, but Messerschmitt fighters on assembly lines in 1943:

These and more pictures of German aircraft manufacturing before and during World War II are available from the Bundesarchiv Picture Database.

Upstream in fuselage assembly, the comparison looks as follows:

In 1934, for Ju-52 fuselages, Junkers used a nose-to-tail assembly line; in 1940, for the Ju-88, a side-by-side line. Today, Boeing 737 fuselage assembly, Spirit Aero in Wichita, KS, appears to be using parallel fixed stations. Fuselage assembly in this context, however, is limited to fastening together sections that have been assembled separately, with automated riveting.

Paxton’s article contains other assertions that are also difficult to accept. He claims, for example, that the abundance of cars in the US spread mechanical skills throughout the population and that these skills made it easier for large numbers of workers to learn how to build airplanes. He quotes the following statistics for the number of people per vehicle in different countries in 1926:

• Australia:  30
• China: 31,871
• Japan: 1,789
• Britain:  49
• France:  54
• Germany: 194
• Italy: 353
• United States: 6

The US was the only country in which almost every family had one car, and American cars of that era were designed to be maintained by their owners. They came with a kit containing the necessary tools and instructions. The US aircraft industry during World War II, however, is known to have employed women in large numbers, as in the following photo of  women installing fixtures and assemblies to a tail fuselage section of a B-17F Bomber (Library of Congress).

If do-it-yourself car maintenance pre-trained World War II aircraft workers in mechanics, then car maintenance must have been done by women. Single women in isolated farms certainly had no choice but to maintain  their cars and tractors, but, in the culture of the 1920’s and 30’s, it is difficult to imagine that women who had a man at hand didn’t delegate changing spark plugs to him rather than learn it themselves. Paxton’s article also asserts that German aircraft production required skilled craftsmen, but most of it during the war was done by forced laborers from occupied countries who were not trained mechanics or machinists.

On the other hand, the article fails to mention two obvious reasons for the superior performance of aircraft manufacturing in the US:

1. Among all the belligerents, the US was the only one with aircraft factories that were out of the enemy’s range. Germany’s ABC program, on the other hand, had defense against air attacks as a central design consideration. Whatever you do to spread out the facilities and protect the supply chain from bombs does not help you in productivity or quality. The Junkers factory in Dessau was bombed in 1944.
2. The US aircraft industry in World War II had a highly motivated work force. Not only were these manufacturing jobs the best these women had ever had, but they knew they were producing equipment for the men in their lives who were fighting for a cause they believed in. By contrast, in Germany, Rosie the Riveter’s counterparts were Polish or French workers building bombers against their will for the worst thugs in history, and they would have been happy to see these planes crash on take-off. In addition, most of them didn’t speak German.

The picture that emerges from the documents I have seen so far is that, in the late 1930s, Junkers had organized production in what is now called pulse lines. Final assembly was divided into operations of balanced durations, so that the planes didn’t move during operations but moved forward in unison at fixed time intervals, with upstream processes and the supply chain organized to support this mode of operation. And this is the Taktsystem that was taught to Mitsubishi Aircraft by Junkers engineers in 1942.

By Michel Baudin Posted in History

# Takt time – Early work at Junkers in Germany

In the TPS Only discussion group on LinkedIn, Joachim Knuf provided the following information, to which I have added a few illustrations:

“Junkers was building an aircraft for infantry support in 1917/18, the J4. After building airplanes in a handcraft mode for some years, this was the first attempt to meet larger demands. Junkers was known for not simply designing a product but the production process along with it. Clearly very lean and practiced by Toyota.”

The founder of the company was Hugo Junkers (pronounced ‘yoonkerz). He died in 1935 and was in no way affiliated with the Nazis, who took away his company and later besmirched his name by claiming association with it. Because the company still bore his name, it is linked in the minds of World War II forced laborers with their experience.

“The J4 was build in modules, incorporating components delivered from outside vendors, incorporating fixtures, templates and gauges for economic benefit. Subsequently, the F13, build in 1919/20 as the world’s first civilian passenger plane, was designed from the start with modular manufacturing in mind. This plane was built for customers around the world, with production numbers as high as 60/month.”

The only surviving J4, at the Canada Aviation and Space Museum.

Junkers F13 in 1925.

“Production was organized to an overall completion schedule. As a result, completion of modules had to be structured and synchronized. Final assembly was organized into six phases, performed at specific fixtures. Highly specialized work teams had a set amount of time to complete their fixture-based task, then moved on to the next fixture to repeat the job, followed by another specialized team (what we think of as a caravan system these days). The increment was the ‘progression interval’ (Fortschrittszeit). Airplanes/modules stayed in place. The result was a finished plane every 9 hours. This approach was shared with Junkers facilities working in other industries.

By 1926 this system was developed to the point that subassemblies could be produced off the main assembly and connected to it with moving lines that moved at set intervals. These intervals were then referred to as ‘Takte’ (plural, ‘takt intervals’). With the new W33/34 (first East-West Atlantic crossing in 1928), there was interest in the US to produce the plane in license, in preparation of which Junkers developed a complete production plan to allow large-scale production, identifying the most economical methods. At that point Junkers had 40% of the international market share. Some years later, Lufthansa orders for the new model Ju 52/3m required the further refinement of the ‘takt method’ (Taktverfahren), incorporating new technology and equipment.”

Junkers W34 at the Canada Aviation and Space Museum.

“After 1933 (and the nationalization of Junkers by the Nazis) this allowed the mass production of airplanes in serial assembly. To produce the required numbers of planes, eventually also using forced labor, Junkers began constructing large subassemblies in decentral locations within 20 miles of the main assembly facility, delivered just in time. Major subassemblies then moved down a ‘takt avenue’ (Taktstrasse) from station to station, remaining a uniform, prescribed ‘takt duration’ (Taktdauer) in each, creating the Junkers ‘Airplane High Volume Series Production to the Minute’ (Flugzeug-Grossreihenfertigung auf die Minute). Changes in takt were used to adjust production volume to demand. Continuous improvement was an integral aspect of this system (which also certified workers on their self-inspection skills).”

A 2010 video entitled Fischertechnik Taktstrasse mit Sortierung depicts a “Taktstrasse” as a transfer line.

# Takt time – More about origins in German aircraft manufacturing

What exactly did the engineers from Junkers tell their hosts at Mitsubishi in Nagoya in 1942 that influenced them so deeply? This is not a subject on which Google overwhelms you with information. I have found so far two German sources that provide at least a context with dates and names: Holger Lorenz, a journalist, and Lutz Budrass, an academic historian, author of a 1,000-page dissertation on the German aircraft industry from 1918 to 1945, now out of print. Lorenz and Budrass both write in German. In English there is a book by Daniel Uziel called Arming the Luftwaffe, but the only reference to Takt in it is in the recollections of a former Junkers worker, who says that his working conditions degraded markedly in 1943 when the Takt system was abandoned in his area, in favor of a moving conveyor.

The featured picture should look eerily familiar to anyone who used small trains for milk runs inside a plant. Lorenz describes it as showing Jumo-211 engines returning from test runs to disassembly. What is odd about the scene is that the train is running outside, with the engines unprotected from the weather. Perhaps the picture was just staged outside on a sunny day.

The ABC program, conceived by Klaus Junkers in 1932-33, called for the transformation of military aircraft manufacturing to mass production, based on Ford methods but with the caveat that the plants should be “fit for air defense.” From the get-go, the factories were designed in the expectation of enemy air raids. For this reason, rather than the kind of concentration you had at the Ford River Rouge plant, it involved multiple assembly halls, 200 to 300 meters apart with trees and green spaces to handicap airstrikes, and a network of suppliers in a circle about 35km away from Dessau, in Köthen, Halberstadt, Staßfurt, Bernburg. Lorenz describes these plants as supplying components “just in time,” but I suspect he is just retrofitting a modern term. “ABC” here refers to multiple locations A, B, C, etc.

Dessau is in the former East Germany, two thirds of the way from Berlin to Leipzig, and a museum is all that is left of the factory. From this location, however, if you operated a milk run through the locations described by Lorenz, using today’s roads, according to Google, it would be 164 km, and take 2 hours and 56 minutes to complete. The route would look as follows:

Of course, we don’t know whether they used milk runs, but their motivation to keep inventories low at the assembly plant was stronger than in more peaceful endeavors: they wanted to reduce the risk of the inventory being destroyed by bombs.

The Junkers plant in Dessau  became the largest  in the entire German aircraft industry, with 40,000 employees at its peak. Lorenz provides the following 1940 layout of the Dessau plant, which I annotated based on his explanations:

Air protection bunkers are under the green areas. The assembly halls are connected by a narrow-gauge railway on the outside.

The leader in building this plant was Heinrich Koppenberg, a metal worker who had risen to top management at the Flick steel company and was in charge of the Dessau facility from its inception in 1934 until 1941. In the following photo, Koppenberg is on the left, showing the plant to Nazi leader Hermann Göring in August, 1939:

According to Budrass, conditions at the plant degraded after Koppenberg’s departure, particularly with the use of forced labor. Production increased, but productivity and quality went down.

But I still don’t know what their Taktsystem was. There is a copy of Budrass’s book at the Stanford Library near here, and I will look at it when I get a chance, and will keep you posted on what I find.

# Takt time: where this strange expression comes from

In the TPS Only discussion group on LinkedIn, Casey Ng posted the following:

“It is quite clear that Takt is a foreign word (外来語) to both English and Japanese.
Its origin could come from German : Taktzeit.
Refer to “Walking Through Lean History” by Jim Womack ( President and founder of Lean Enterprise Institute:

‘By the late 1930s, the German aircraft industry had pioneered takt time as a way to synchronize aircraft final assembly in which airplane fuselages were moved ahead in unison throughout final assembly at a precise measure (takt) of time.’

Therefore, Toyota could have adopted the term and application from Mitsubishi who had technical link with the German in aircraft manufacturing.
But Toyota did breathe new life to the concept of takt by integrating it to the flow principle and inventory reduction of JIT. Therefore, any attempt to implement JIT without proper understanding of takt with Taiichi Ohno’s precise definition of takt time could fail.”

To which Bertrand Chauveau added:

“Takt is a German word

Casey, you are right. It is a German word used in music to describe the rhythm. Mitsubishi brought it back to Japan. Association of Japanese manufacturers deployed it throughout the industry. Thus Toyota adopted and adapted the concept to their production.”

“Regarding the German origins of “takt,” I have never heard any of the Japanese consultants I worked with say where they thought the origin was, but a consultant from JIPM did say to me once that Shingo used the term, and so Bertrand’s explanation makes sense.”

Following are the results of my own research into the matter:

Takt is indeeed a German word, designating a bar on sheet music, but also an engine stroke as in Viertaktmotor (four-stroke engine), and the interval between trains on a line where they run regularly (picture by David J. Anderson), as shown below:

Lean implementers in Germany today, however, are just as confused about it as Americans, and I have heard some refer to Takt as the process time.

But how exactly did “Takt” migrate from Germany to Japan? I think the key reason the Japanese consultants Frederick worked with didn’t dwell on it is that it happened during World War II, and that Japan’s war time alliance with Nazi Germany is not a source of pride.

Digging further on the input from Casey and Bertrand, I found in Americanization and Its Limits a chapter by Katsuo Wada and Takao Shiba reporting that the military aircraft arm of Mitsubishi learned about the German “Takt system” from Junkers engineers in 1942, and had implemented it in the Nagoya works in fuselage assembly by 1943, under the name of zenshinshiki (前進式?). From a contemporary observer’s description, it looks very much like the pulse line system currently used for military aircraft at Boeing, with fuselage sections assembled at fixed stations and moved at a fixed interval — the Takt — to the next station.

This is to be contrasted with the moving assembly line concept used for aircraft also in World War II by Ford in Willow Run, MI, for the B24, and currently by Boeing for commercial aircraft. And it is not the same concept as takt-driven production today. But there are also accounts in German Aircraft of the Second World War of the German aircraft industry using moving lines for subassemblies during the war.

The Nagoya location of this Mitsubishi plant may not be coincidental to the transfer of the term to Toyota, which is still headquartered in that area. It may have been carried in the heads of unemployed military aircraft engineers joining Toyota after the war.

For the German part of the story, in German Aircraft of the Second World War, J.R. Smith and A.L. Kay, in their discussion of the Ju-88, explain “In August 1938, Ernst Udet laid down the Takt system of construction for all large state-owned firms such as Junkers and Arado…”

A Ju-88 flying in 1936

I also found the following picture of a Ju-88 assembly line in 1941, which suggests that the fuselages move sideways between operations rather than nose-to-tail:

Ju-88 Assembly Line in 1941

This is where the trail ends for now. Udet committed suicide in 1941, and was therefore not involved in the transfer to Mitsubishi. I have yet to find a detailed description of the Junkers “Taktsystem.”

# Takt time: can it be universally applied to all types of production?

This is the question Casey Ng asked in the TPS Only discussion group on LinkedIn. He elaborated as follow:

What are the essential conditions to implement takt time successfully? What are the cases when it fails and if you refer to the fundamental principle of takt and yet couldn’t find the solution? Then what are the exception areas and what alternate solution can be used?

To date, it has generated 43 comments, many with the high level of depth and the implementation examples that are characteristic to this group. It is a new LinkedIn group, with only 118 members — compared with 151,503 for Lean Six Sigma — but passionate and providing meaty technical content. I recommend it in general, and this discussion in particular. Here, I will be including only my own contributions on takt time, and its relevance to the following:

## 1. Monuments

With monuments — the very large machines used for heat treatment, electroplating, painting, cutting of sheet metal, etc. — you usually have to load multiple parts simultaneously in order to meet demand, but these parts often do not have to be identical. I don’t recall anyone mentioning this in the earlier comments, but the parts that you load together can be a matching set rather than a batch. If your takt times are long enough, as, for example, in aircraft production, you can actually process one plane-set at a time, to takt time.

## 2. Gigantic products with long takt times

Gigantic products, like oil tankers, with takt times of six months or more, are built out of vertical hull slices made at much shorter takt times in a shop, and then welded together in the dry dock. Pioneered in the US with Liberty Ships during World War II, this is now standard shipyard practice, and enhances of the repetitiveness of the process, applying the concepts of takt time and one-piece flow.

## 3. Refueling outages in nuclear power plants

I am puzzled by Todd McCann‘s use of the takt time concept in the context of nuclear plant refueling outages, a problem I had the opportunity to work on 20 years ago in France, not in the US. I don’t know who the top performers are in this area today. At the time, it was a tie between the French and the Japanese, at about three weeks from shutdown to restart for one reactor, which is substantially longer than the 193 hours you were quoting for 2006, assuming that the work continues 24 hours/day, 7 days/week.

The French performance was accomplished by standardization. They had 55 reactors with only two designs, producing respectively 900MW and 1300MW, run by a single company. The procedures were the same everywhere, with any improvement quickly shared. The Japanese performance was based on using techniques from TPM. They had nine different reactor designs, run by different utility companies.

Even though they had the best performance in the world, I saw many opportunities for improvement, based on borrowing techniques from SMED, improved planning and scheduling for materials, tooling, and the 1000+ contractors involved, and operational details. Such a detail, for example, was security. Their procedures were effective at controlling access, but inefficient, with utility employees at all levels spending too much time getting contractors into and out of the facility.

The concept of takt, on the other hand, did not strike me as particularly relevant, given that a refueling outage is a yearly burst of intense activity for any given reactor, as opposed to a repetitive process.

## 4. Rate work versus response work

More generally about takt time, most businesses have both what my colleague Crispin Vincenti-Brown called Rate Work and Response Work. In manufacturing, if you do a Runner-Repeater-Stranger analysis of your products, Your Runners and Repeaters are rate work; your Strangers, response work.

Runners are products with enough volume to warrant a dedicated line. Repeaters are products that you group into families that, in aggregate, have enough volume for a line. Strangers are all the other products, including R&D prototypes, sample quantities of new products, spare parts for obsolete products, and any other special request. Even in aggregate, they account neither for a high volume nor for high revenue, but you still must produce them promptly. They require a small job-shop set up with your most flexible equipment, staffed with your most versatile operators, and its own operating policies.

While takt time is fundamental to line design for Runners and Repeaters, it isn’t much use for Strangers.

## 5. Non-repetitive operations

I have a hard time seeing the relevance of takt time in the absence of repetitiveness. In an assembly process, the takt time gives you an upper bound for the process time at each operation. As you broaden the mix of products you assemble on the same line, it becomes more difficult to balance the work among stations. Past a certain point, you are better off using approaches like bucket brigades, a.k.a. bump-back system, or even a yatai, which are not based on takt time.

## 6. Takt time and its calculation

Outside of mathematics, concepts are not reducible to formulas. Time/Demand is the way you calculate takt time, but it tells you neither the rules by which you are supposed to use that number nor how it maps to shop floor activity.

In mass production plants, managers use the inverse of this ratio: Demand/Time, which gives you the same information. Mathematically, working at a takt time of 1 minute and making 60 units/hour (uph) is equivalent. Yet, you and I know that, depending on whether the manager thinks the plant is producing at a takt time of 1 minute or making 60 uph, the shop floor will be radically different.

If you think in terms of uph, it doesn’t matter if nothing comes out for the first 59 minutes of each hour as long as all 60 come out in the end. If you think in terms of takt, 1 unit will come out like clockwork every minute.

What this says is that there is more to takt time than the formula. This is discussed extensively in Lean Assembly, with the following definition of takt time:

“Assuming we complete the product one unit at a time at a constant rate during the net available work time, the takt time is the amount of time that must elapse between two consecutive unit completions in order to meet the demand.”

As I recall, this is,more formally, the way Ohno described the concept in Toyota Production System.

## 7. Takt-driven production as the ideal state

The takt time allows you to define an ideal state, that John Shook and Pascal Dennis call True North, but that I prefer to call takt-driven production. In this state, you perform all operations one-piece at a time with process times that exactly match the takt time, and with instant transfer to the next operation at every beat. Of course, it is never perfectly realized, even on an assembly line. Real lines can only be approximations of it. The point is that it gives us a direction.

All deviations from takt-driven production translate to Ohno’s waste categories, overproduction, waiting, excess inventory, etc. Since any local project that move production in this direction eliminates waste, it can be undertaken with the confidence that it contributes to global improvement and is not sub-optimization.

## 8. Chronos, kairos, and takt time

Joachim Knuf : “… The ancient Greeks differentiated between two types of time: chronos (chronological, sequence of intervals, typically of equal extension) and kairos, best thought of as ‘the opportune moment.’ In this case, intervals begin and end under sets of conditions. This concept applies, for example, to healthcare, when next process steps are initiated by a preset configuration of values (patient’s blood pressure, glycemic index, bowel movement), not by elapsed time…”

I had never heard of Kairos, but, if the ancient Greeks made the distinction between Kronos and Kairos, why shouldn’t we? There is a rich toolbox associated with the pursuit of takt-driven production. Where the concept of takt does not apply, we can’t use these tools. As you said, extending usage of the word to Kairos-driven activities just adds confusion. These activities need different tools, and Casey pointed out some of them in his comments on Strangers. Let us keep different words to hang them on.

# Yet another (wrong) definition of takt time

This is from a blog post published today that claims to clarify what a takt time is:

Takt Time:  This is the rate of time at which a product or service is being purchased.  For example, a Nissan commercial mentioned that every minute, someone in the world buys a new Nissan.  Selling a car every minute is an excellent example of takt time!

Writing a definition for a thing or an idea is tricky. Following Aristotle, I would say that you have done a good job if you have described what kind of a thing it is and how it differs from other things of the same kind, using terms your reader already understands.

In this definition, takt time is described as a “rate of time.” If there were such a thing as a rate of time, in what units would it be expressed? In production, a rate is expressed, for example, in pieces per hour; a time, in minutes or seconds. Takt Time, as its name suggests is a time, not a rate, and certainly not a rate of time, whatever that may be.

This definition then relates takt time exclusively to “a product or service [..] being purchased,” and gives the example of a Nissan being bought every minute in the world, suggesting that 1 minute is the takt time of a Nissan. Incidentally, if this figure were true, Nissan would sell about 500,000 cars/year, versus the 4 million it actually sells.

Takt time, as we use it in manufacturing and industrial engineering, is in fact not a parameter associated with just a product but with a production line making this product. Given the demand that is given to it and the amount of time that it actually works, the takt time of this production line for this product is the time that must elapse between two consecutive unit completions.

If a line is expected to produce 400 units of a product in a 400-minute shift, then, if you stand by the last station of the line, you will see one unit come out every minute, meaning that its takt time is 1 minute. If you switch from working 1 shift/day to 2 to meet the same demand, you double the takt time to 2 minutes.

This is why it is calculated as follows:

$Takt\, time(Product, Production\, line)=\frac{Net\, available\, production\, time}{Demand}$

It has a numerator and a denominator, and both matter. They are obviously calculated for the same time period.