Category Archives: Unit Proliferation

The Pseudo-Inch

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By The Metric Maven

Bulldog Edition

I have a friend, Pierre, who has a passion for woodworking, but a passion for metric?—not so much. My knowledge of woodworking is at best minimal, but Pierre does his best to enlighten me. One evening I received an email from him after he had watched a woodworking program by Roy Underhill.  Roy is an American, and a bit of legend in woodworking as I understand it. During the program, Roy explained a Swedish method of teaching called sloyd. My friend Pierre then related:

The original Swedish drawings in the book of exercises he used were measured in metric. Underhill says, “I took up woodworking so I wouldn’t have to learn metric.” Thought you’d want to know that.

Next, Underhill was showing how to measure 2 cm over on a board using a Swedish wooden folding rule. He said he got it from some visiting Swedish woodworking friends, because his American one doesn’t have centimeters on the back. He said, they said, and this is really the part I wanted you to know, that in Sweden, his woodworking friends use only inches.

Then, he flipped the Swedish folding rule over, and it showed inches. Here’s another interesting part, I hope you aren’t asleep yet.

The Swedish “inch” is bigger than our inch. Holding the rules one over the other, you could clearly see the Swedish “inch” is about 1/16 bigger.

WTF, man?

Well, the problem is, there is really no such thing as “an inch.”  Why do we think that an inch exists?—well, therein lies the tale. The Wikipedia entry for “the inch” has an enlightening “inch converter” which was used before the age of the metric system. Here is the illustration:

19th Century Inch Converter

19th Century Inch Converter — Wikipedia Commons

One can see that “the inch” has many different lengths in the 19th century. Many of them are considerably different in length. Note the Moscow and Russian inch are not even close to one another. Here’s what I have surmised from this converter about inches:

  • Hamburgh – Inch divided into 8 parts. 1 inch ≈ 23.2 mm
  • Austrian – Inch divided into 8 parts. 1 inch ≈ 25.8 mm
  • Itallian – Inch divided into 8 parts. 1 inch ≈ 28.3 mm
  • Bremen – Inch divided into 10 parts. 1 inch ≈ 23.7 mm
  • Swedish – Inch divided into 12 parts. 1 inch ≈ 24.3 mm
  • Turkish – Inch divided into 12 parts. 1 inch ≈ 31.3 mm
  • Bavarian – Inch divided into 12 parts. 1 inch ≈ 24.0 mm
  • Spanish – Inch divided into 12 parts. 1 inch ≈ 23.0 mm
  • Portuguese – Inch divided into 12 parts. 1 inch ≈ 27.0 mm
  • Moscow – Inch divided into 12 parts. 1 inch ≈ 27.7 mm
  • Russian – Inch divided into 8 parts. 1 inch ≈ 44.1 mm
  • Amsterdam – Inch divided into 12 parts. 1 inch ≈ 23.5 mm
  • Rhynland – Inch divided into 12 parts. 1 inch ≈ 26.1 mm
  • French – Inch divided into 12 parts. 1 inch ≈ 27.0 mm
  • Fr. Metre – Centimetres divided into millimetres
  • English – Inch divided into 32 parts. 1 inch ≈ 25.3 mm
The “inch” is a perfect example of what I call  a retread unit. This is a unit with a name that is used over and over for different quantities, which renders it meaningless as a standard.
This lack of a clear international definition of the inch, produced a strange misunderstanding in the early part of the Twentieth Century between Americans, British and Australians–who were the contractors:
In 1909 the American firm Pratt and Whitney was contracted to supply all the equipment for the Lithgow plant to specifications that  would ensure interchangeability of components with British rifles. But the parts would not fit because no one told the Americans that the British drawings used two different standards of length: dimensions above 2 inches were expressed in inches aligned with the imperial yard; but dimensions below 2 inches were based on the `Enfield inch’, a standard used by the Royal Small Arms Factory at Enfield. (For Good Measure Jan Todd 2004 pg 58)
Here is the history of the Swedish inch according to Wikipedia:
In Sweden, from 1855 to 1863, the existing Swedish “working inch” of ≈24.74 mm was replaced by a “decimal inch” of ≈29.69 mm which was one-tenth of the Swedish foot. Proponents argued that a decimal system would simplify calculations. However, having two different Swedish inch measures (and the English inch on top of that) proved to be complicated. So in a transition period between 1878 and 1889 the metric units were introduced as the overall standard measures. However, the various inches survived some time in building and construction trades.
click to enlarge image

Originally the Anglo-Saxons used their smallest standard, the barleycorn, to define the inch. We still use barleycorns to define shoe sizes in the US. The standard was three barleycorns in a row make an inch. I call this “The Barleycorn Inch.” The barleycorn is also called the grain. There are 7000 grains to a pound. In the 20th century, the British and Americans decided to define their inch as exactly 25.4 mm. It is sometimes called the “Industrial Inch.” This is what Americans call “The Inch.” This inch was decimalized in many industrial applications and is found on many, many US technical drawings. The decimalization of the inch is the basis for our machine tools, yet finding a ruler in the US with decimalized inches is almost impossible. Our educational system doesn’t even teach decimalized inch units and how they are used by industry. The fascination with fractions in this country is beyond my understanding.

I have converted my engineering work to be entirely metric, which can cause heartburn for some American vendors. Recently I finished a PCB design for a broadband microwave device. I sent a PCB fabricator gerber files and metric drawings of the device to be fabricated. They requested I give them drawings with dimensions in inches—I demurred. They asked again—again I told them no. Their third email to me pointed out that inches were what their equipment was calibrated to, and what they are trained to use, are used in the US, and they wanted inches.

Dimensional Standard for Barleycorn Inches

The PCB files I sent actually were in inches as forced by US industry, but the drawings were not–so why was the vendor so insistent that I provide inch drawings? Well, in Engineering, engineering drawings define the controlling dimension. The controlling dimension is the one to which the manufacturer is expected to conform. If I have a 100 mm drawing dimension, that is what the length is supposed to be, with a tolerance in mm, not 3.937 inches and a tolerance in mils. The conversion from inch to mm is exact, the conversion from mm to inches is inexact. The vendor did not want to be held to the accuracy required in mm when they had inches on their fabrication equipment.

The point I made to them is that the controlling dimension on all engineering drawings in the US is actually metric. This is because we use the Industrial inch in the US. The definition of the US inch is 25.4 mm exactly. All the “inches” of the vendor’s equipment are calibrated and controlled by the meter, so the controlling dimension of all US drawings in inches, is actually in terms of mm (i.e. meters), we just don’t acknowledge this.  The situation ended up resolving itself, and the boards were successfully fabricated. As a country we pretend that we use something called “the inch,” but it is derived from a metric standard. We use metric as our base standard, but do not adopt the convenience of the actual metric system, preferring to pretend we have “our own American/Standard” system. This is delusional.

The power the inch has over US citizens and others appears to have caused early users of metric to impose vacuous imperial conventions on the metric system. You will note that on the “inch converter” from Wikipedia the centimeter also appears in the list. As I have explained in detail in other blogs, the centimeter impedes the ease of use and soils the elegance the metric system offers. The use of millimeters only, allows for a simple and accurate implementation of metric—often without decimal points. This is experienced by Australian construction workers every day. The fact that Roy Underhill doesn’t understand the power of using millimeters, and slavishly uses centimeters instead, makes him less than a legend to me. He simply embraces folklore. The centimeter is the perfect example of an unnecessary division which appears to exist only to preserve an unnecessary and ill-defined unit of magnitude called “the inch.”. The centimeter is but a pseudo-inch, demanded by tradition and not by necessity. Its utility has proven to be non-existant in practice. Remember friends don’t let friends use centimeters. And The inch?—the definite article?—well, it’s much like fairies, and other mythical creatures, it only exists in our imagination.

Updated 2013-01-31

Related essays:

Metamorphosis and Millimeters

Building a Metric Shed

If you liked this essay and wish to support the work of The Metric Maven, please visit his Patreon Page and contribute. Also purchase his books about the metric system:

The first book is titled: Our Crumbling Invisible Infrastructure. It is a succinct set of essays  that explain why the absence of the metric system in the US is detrimental to our personal heath and our economy. These essays are separately available for free on my website,  but the book has them all in one place in print. The book may be purchased from Amazon here.


The second book is titled The Dimensions of the Cosmos. It takes the metric prefixes from yotta to Yocto and uses each metric prefix to describe a metric world. The book has a considerable number of color images to compliment the prose. It has been receiving good reviews. I think would be a great reference for US science teachers. It has a considerable number of scientific factoids and anecdotes that I believe would be of considerable educational use. It is available from Amazon here.


The third book is not of direct importance to metric education. It is called Death By A Thousand Cuts, A Secret History of the Metric System in The United States. This monograph explains how we have been unable to legally deal with weights and measures in the United States from George Washington, to our current day. This book is also available on Amazon here.

American Software vs. Metric or Mormons Making Coffee

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By The Metric Maven

It is my understanding that during the Bejing Olympics the United States Olympic Committee (USOC) sent measuring cups and spoons to China. This was done because the Chinese could cook recipes from anywhere else in the world but not those from the US.  The non-metric units of the US were a complete bafflement to the hosts, and when the Olympics were over, they just threw the cups and teaspoons away seeing them as useless.

I began cooking with metric about three years ago. It took me a while to understand that I needed a scale with a digital readout in grams. I realized that metric recipes generally use mass instead of volume for dry ingredients. The best chefs do this also. The surprising part was that because of the fact that 50 milliliters of water weights 50 grams, I could actually estimate using the mass of many liquids also. After I became used to using the digital scale and it’s tare function, I found cooking in metric vastly easier, quicker, and more enjoyable than it had been in imperial.

My father has been interested in cooking his entire life. He uses a software package to index his recipes. During a recent visit to his home, my father marinaded steaks and served them for supper. I had not tasted steaks made this way since I was a boy, and later asked for the marinade recipe by email. He sent me the recipe in imperial units as I would expect and then said he had included a metric version from the program so I would not have to convert it. Below is a reproduction of the metric recipe:

After I saw this I wrote my father an email, and asked if he had created this metric recipe  as a joke. No, he assured me, it’s how it came out of the recipe program. I was just gobsmacked by the use of fractional values of centiliters, deciliters and milliliters. According to the metric recipe this would make one cup of marinade.

This strange metric usage made me think of a story told to me by a deceased family friend, known as Skeez, about his experiences in World War II. He talked about riding in troop trains across the US when he was in the military. He gushed and gushed about the great food the women would have prepared for them at each rail stop. Word had “gotten around” that the food at all the Utah stops was good—but don’t drink the coffee. Mormons are forbidden from drinking coffee, but when they were catering for the government, and were required to brew it, the coffee was not remotely as good as the food..

In fact, the coffee served by Mormons was so awful, that considerable speculation went into the method used to make it so completely unpalatable. Some argued that they reheated the same giant container of coffee over and over during the week, and just added more as it decreased in volume. Others thought they just re-used the coffee grounds and added new when it didn’t look black enough. For me “Mormons Making Coffee” was a metaphor for people trying to implement something about which they had only a very slight acquaintance or understanding, and no working knowledge. Like an American presiding over a cricket match.

Whoever programmed the recipe software my father owned, had proved to me that he was like a “Mormon Making Coffee,” but more specifically he was an American Using Metric. There could be no certainty how an American might imagine metric should be used in cooking, and as we see, anything could happen. The two hallmarks of the metric system which make it elegant for cooking, is that it can be implemented to whole value (integer) numbers and only a simple set of prefixes need to be used. It was clear that the confused, and nearly incomprehensible, American measurement vernacular had been imposed on the metric recipe. The use of 1 1/8, 2 1/2 and 1 1/4 with metric values was ultimate proof. As the saying goes, there is no crying in baseball, and no fractions in metric. Metric recipes generally use whole numbers and milliliters–only. And certainly not fractions. Generally spices are measured in volume as indicated, but not with fractional numbers. The brown sugar would be measured in grams. Let’s take this simple recipe and write it as I would have expected to see it.

Don’s Soy Sauce Marinade

125 mL LaChoy Soy Sauce
125 mL Orange Juice
30 mL Lemon Juice
12 grams (15 mL) Brown Sugar
30 mL Salad Oil
3 mL Pepper Sauce
1 Clove garlic, crushed
1.25 mL Black Pepper

Combine ingredients. Use to marinate beef, pork, or chicken before grilling or broiling. I usually put it in a Ziploc bag with the marinade for 2 to 4 hours before grilling…..for a little different flavor add 30 mL of Worcestershire sauce.

Yield 300 mL

This is the best I could do with this conversion. You will note that other than the black pepper, I was able to use whole numbers for the rest of the ingredients.

This episode in my life illustrates something I did not appreciate until a few years ago. Although the metric system is much simpler than the, bloated, and uncorrelated set of units used in the US today, metric should still be even simpler. There are metric prefixes that should be eliminated, which I call the prefix cluster around unity. More formally it’s Naughtin’s 4th law. Some prefixes with units, like the centimeter the centiliter, deciliter should be vanquished. The use of prefixes that are spaced by a factor of 1000 seems to work very well, and is about as simple as it gets for metric system implementation. In cooking, the milliliter is probably all you need for volume, the gram for mass, and the millimeter for distances, and that’s it—done!—nothing else to learn!

American Interpretation of using The Metric System in Cooking

With a metric recipe and proper instructions—perhaps even Mormons could successfully make palatable coffee. But not if that metric recipe was created by imperial to metric conversion software, which had been written by American programmers. Without instruction in the metric system from childhood, and its mandatory and efficient adoption in the US, our software designers will probably continue to use metric in an obtuse manner, and continue to create the illusion that the metric system is complicated, when it’s a paragon of simplicity.

Updated 2012-11-10  Fixed quantities in recipe.

If you liked this essay and wish to support the work of The Metric Maven, please visit his Patreon Page and contribute. Also purchase his books about the metric system:

The first book is titled: Our Crumbling Invisible Infrastructure. It is a succinct set of essays  that explain why the absence of the metric system in the US is detrimental to our personal heath and our economy. These essays are separately available for free on my website,  but the book has them all in one place in print. The book may be purchased from Amazon here.


The second book is titled The Dimensions of the Cosmos. It takes the metric prefixes from yotta to Yocto and uses each metric prefix to describe a metric world. The book has a considerable number of color images to compliment the prose. It has been receiving good reviews. I think would be a great reference for US science teachers. It has a considerable number of scientific factoids and anecdotes that I believe would be of considerable educational use. It is available from Amazon here.


The third book is not of direct importance to metric education. It is called Death By A Thousand Cuts, A Secret History of the Metric System in The United States. This monograph explains how we have been unable to legally deal with weights and measures in the United States from George Washington, to our current day. This book is also available on Amazon here.