The Metric Mess is Hard Wired in The US


By The Metric Maven

Bulldog Edition

Skeez was a person who seemed to be born interesting. He obtained his nickname from a character called Skeezix in the comic strip Gasoline Alley. The comic strip itself is unusual in that Skeezix arrives as a baby on a doorstep and ages as time goes on. Skeez spent much time at his cottage on the shore of a nearby lake. One day I noticed a new bust among his eclectic collection of objects; it was Charles Dickens. Skeez then told me that Dickens had a story about an innkeeper who was so cheap he counted the number of beans he put into his soup, and that’s where the term “bean counter” arose. He was as close to a polymath as I have ever known. When he passed away I ended up with small gargoyles that he had brought back from France during World War II. I have an African shield with a weapon which was used to kill tigers, as well as other books and notes he left behind.

Recently I ran across a an RCA Radiotron Reference Book from 1940 which Skeez had owned. Inside, it contains a small snapshot of how the metric system was viewed by electrical engineers in 1940. It appears that US engineers saw the metric system as a simple drop-in substitute for Olde English measures. For instance, under pressure they equate pounds per square inch to Kilograms per square centimeter. No pascals. The equivalence of kilograms (mass) with pounds (force) is a strange misunderstanding in a reference like this—unless they meant Kilogram-force. It is clear that again Americans see the centimeter as a pseudo-inch and just substitute away without any measurement introspection. I’ve not found a millimeter mentioned in this reference.

It also has a list of miscellaneous conversions that have a couple of interesting aspects. First I had no idea there was a unit of metric horsepower. Apparently notion of horsepower was still considered so important in 1940 that a metric version needed to be defined. Apparently metric horses have less strength than Olde English horses. The definition does not seem to even involve a horse:

DIN 66036 defines one metric horsepower as the power to raise a mass of 75 kilograms against the earth’s gravitational force over a distance of one metre in one second;[13]

The other odd aspect is that meters show up with an er ending, but litre is spelled with re. I’ve often wondered when it was decided, and by whom that in the US we would use er rather than re. Here the situation is mixed.

What really caught my attention, and is the actual subject of this essay, are the tables on wire.  American copper wire is designated in American Wire Gauge (AWG). I have made my view known concerning the vacuous non-term gauge in a previous essay. We note that along the left column is the AWG number. AWG was first used as a designation in 1857. The diameter of the wire is then given using the informal feral unit known as the mil. A mil is a slang term for one-thousandth of an inch—at least in the US. In metric countries it’s a slang term for a millimeter as I understand it. As the gauge number increases, the diameter decreases.

There is also a column to the right of the diameter of the wire in mils, which is the area in circular mils. Let’s take an easy example, say AWG 10, which is a solid wire with  a diameter of 101.9 mils. Now we know the area of a circle is π multiplied by the radius squared.  The answer to the computation is 8155 square mils. But wait–the value in the area column is actually 10 380 circular mils. Well, that’s because apparently our engineering founding fathers, in their infinite wisdom, decided that dividing the area up into the number of circular areas of one mil was the best way to do it. To get circular mils you just square the wire diameter in mils. This produces a value that is not directly usable for any common engineering calculations. The resistance of a solid wire is proportional to the cross-sectional area, and circular mils are essentially a gauge number for area and not a defined area. We have inherited this strange way of determining the area of solid copper wire without questioning its sanity. It also illustrates once again that our Olde English set of measurements has nothing in common with a system. To make matters worse, Wikipedia decided to use the term kcmil for kilo-circular-mil in their wire table. I wish metric prefixes would only be used with metric units, and not feral ones, or medieval ones.

Another page in the RCA Radiotron Reference Book has the number of winding turns which make up a linear inch. For example, the Brown and Sharpe (i.e. AWG) Gauge Number is given on the left. We then see that for enamel coated wire one needs 7.6 turns of AWG 8 wire to have a coil which is one inch in length. This data is useful for computing how long an inductor might be for an electrical engineer.

If one were rationally using the metric system, one could easily compute any of these values from a table which gives the wire diameter in millimeters and the area in millimeters squared. If the wire manufactures were to use preferred numbers with metric diameters, then it would simplify matters further. Their would be no more indirect designation of sizes with meaningless gauge numbers. The values would be directly understandable in millimeters. Let’s suppose we have a wire of 1.25 mm diameter, we would know immediately that ten turns is 12.5 mm. We could use AWG 16 which after we consult the table is seen to have a diameter of 50.8 mils. We then know that ten turns is 500.8 mils, divide by 1000 to get the value in inches or 0.5008 inches. Alternatively, we could have started with a direct metric designation of 1.291 mm and ten turns is immediately seen to be 12.91 mm. Starting with the metric diameter, one knows this is the width of a single turn. Using this, one can quickly evaluate 1/1.291 mm on a calculator which is 0.775 turns per millimeter. To get 10 millimeters it would take 7.75 turns. start with a metric wire diameter and one can quickly compute anything one needs–using common mathematics.

Incidentally the gauge designations for copper wire are not standard across types of wire, so one can’t be certain what diameter other wires might be when  given a gauge number. Clearly,  if the diameter of a wire in milimeters is given, or another appropriate metric length (e.g. micrometers), this allows one to immediately compute any appropriate parameter. Here is an illustration from a vendor who sells wire in Australia:

The wire industry in the US has been using this kludged up system since 1857 and has done nothing to introduce reform. This clearly shows to me that one needs to have a government mandate, like that implemented by Australia, which mandates metric. The voluntary part for industry is how they will introduce metric. If they have any sense they would take the opportunity to reform their industry with preferred numbers, or in some other rational manner. Standard DIN Sizes using ISO6722 in terms of mm² look like a good idea to me. But how they would implement the change would would be up to them—and in ‘merica they just might use “soft” metric and preserve familiarity over simplicity along with 19th century measurement practice. Until then, this mess is hard wired in the US.

Evanescent Measurement Policy

By The Metric Maven

Bulldog Edition

One day I was visiting a production plant which creates and molds materials for electronic components. I noted they were measuring the length of the component in barleycorn inches with a few zeros at the front of the decimal. The data was being entered by hand onto a paper table held with a clipboard. I indicated that it would be wiser to measure in millimeters so the data didn’t contain so many leading zeros and provide such an easy opportunity for error—and there would be less redundant digits to write down. They next measured the mass of the object in grams with a scale that went way way down into the microgram range. It also had a large number of leading zeros to the right of the decimal point.

After they had obtained the mass (in grams) and volume (using inches) they computed the density or mass/volume. I was told it was expressed in grams per cubic centimeter. I did have an attack of the vapors realizing they were using pigfish measurement, and then converting to metric, and worst of all used cubic centimeters. The metric system has a nice unit for volume called the liter. A cubic centimeter may be a volume dimensionally, but it is a milliliter which is an appropriate volume unit in my view, and identical to a cubic centimeter.  The cc is a part of the cgs system, and has long been abandoned.

Along the way I was shown the dielectric material in granular form before it undergoes processing for later fabrication into electronic parts. The materials chemist was pleased to tell me that they were all created to be about 100 microns in diameter. I cringed slightly, and then said “you mean micrometers?  Micron is a term from the 19th century and is not expressive.” Little was said after my comment and we moved on.

During a discussion about part fabrication difficulties, mils (thousandths of an inch) were bandied about constantly. I finally asked about the surface roughness of the material. I had determined it could contribute to the problems they were having. I was given a value in microinches. A metric prefix with Ye Olde English?—sigh. I could only reply with “I have no idea what size that is.”  I was then quoted a value in microns. Again with the microns? I wanted to do a face-palm, but refrained.

I have been on many tours of engineering and production facilities. It was only when I was at this particular establishment that I realized, I’ve never toured ANY company that has a measurement policy or measurement coordinator. It is not discussed, contemplated, seen as a concern—nada. When I bring up metric measurements, it is as if my statements and questions vanish into a black hole of indifference.

A week or so later another engineering client sent me a drawing which has a part made from a similar ceramic material. The dimensions on the drawing were all in inches, but in the notes, the metalization thickness on the part was called out in micrometers. The second note described the density of the part in grams per cubic centimeter (g/cc). I just stared at the drawing, and thought about my recent visit. Inches, micrometers, and the cgs unit g/cc all on the same drawing? Three different measurement types on one drawing. Why does this strike only me as bad engineering practice?

Density is mass per unit of volume. The density value on the drawing was 3.73 g/cc +/- 0.1%. In SI the milliliter (mL) would be an appropriate volume which would be 3.73 g/mL +/- 0.1%.  The cgs/SI/Ye Olde English mixing of units has become so accepted in the US that it goes without notice apparently. As I said, thus far I’ve never seen a company that has a “Measurement Coordinator.”  This would be a person who would help create a measurement policy and apply Naughtin’s Laws as well as the rule of thousands. That person would examine, simplify and coordinate measurements to maximize the understanding of data presentation and reduce possible mistakes—and implement the metric system. It never occurs to business management that measurement coordination could be a cost or efficiency issue.

I’ve always been tasked with design work, and never anything which would involve setting measurement policy. Pat Naughtin was the first to discuss the fact that NASA’s measurement policy is “change to metric, if you want to, use centimeters and/or millimeters, if you want to.” In other words NASA simply didn’t see measurement policy as a problem which is in need of any coordination or effort. This means they don’t see it as a problem at all, and so they do not have a measurement policy. Unfortunately the current former head of NIST also has a “do your own thing” measurement policy.

In the back of my mind I wondered what the reaction of one of my clients might be if I brought up the possibility of a measurement coordinator. I had concerns about it, and the next time I was on the phone with Sven, I asked him what he thought the reaction might be from management and a group of engineers.

Sven: “They would not see any need for it, and they would look at you as if you were wearing a gunny-sack with a belt and sandals, had a long beard, and were holding a sign which read REPENT!”

MM: “I was afraid you would say that.”

Every engineer I know believes they understand measurement units and measurement. There is no need for a policy, we “learned” it all in college. Some co-workers have indicated to me that metrology is what people do who really don’t have any engineering talent. You can imagine how my psyche greeted that notion. I’ve met way too many “engineers” who embrace measurement methods which are ad hoc and unsound. They chase down blind alleys of impromptu measurement and waste time. But as long as a product “gets out the door” and appears to work—there is no problem here—move along.

Isaac Asimov in an essay called Forget it! pointed out that often measurement units that should have been abandoned long ago, continue to be used. The units are also only imperfectly forgotten, which leads to an even more chaotic usage. The cgs system was abandoned many years ago, but the inertia of unrestricted usage propels them into the future.

I spoke with a medical researcher at a block party last summer, and mentioned metric. He proudly stated he uses metric in his work and cited the cubic centimeter. I pointed out that the cc was part of centimeter-gram-second system, and the cgs system is not compatible with SI. He should be using milliliters. He looked at me as if I was daft, and going out of my way trying to be annoying.

The technical drawings I received with cc’s on them, show an incomplete ability to forget cgs, as do the density measurements performed by another client. Recall they first started in inches with a long number of zeros past the decimal point, then converted the inches to cc’s, and then finally computed grams/cc for a density. The inch is Ye Olde English, the gram is SI, and the cc is cgs. Both the inch and cc should be forgotten and eschewed; but the 10th, 14th and 19th  centuries live on in the US, never forgotten or allowed to be. They are the products of the “unexamined engineering life.”

I wholeheartedly agree with Pat Naughtin’s call for measurement coordinators and measurement policies in industry. As he himself pointed out, often questions of measurement are considered so minor, that scales and other measurement instruments are chosen and ordered by secretaries or interns. To show they are giving the company the most value, they order dual or multiple scale measurement devices. This perpetuates the farrago of units in use.

NASA demonstrated itself to be immune to the notion of measurement coordination even after the Mars Climate Orbiter disaster. The much less well-known DART “mishap” even appears to have been obfuscated with a mantle of junk prose. It was more important for NASA to deny there is a need for measurement coordination, than to address the problem. I really have no idea what it might take for the technical community, educators and the public to realize that measurements are the real currency upon which our modern technical society operates, and there is a need to coordinate and simplify them. I can only hope for the US metric coma to finally recede, the country to wake up, and then finally address the problem.