In Favor of the Inch by J.R. Beall
Noc long ago, while at a woodworking show. I overheard a great guru of contemporary woodworking lambasting the English system of measurement. He railed against the idiocy of dealing with fractions, and against the strange and senseless units of measurement this system employs. I held my tongue, as is my custom, but have since thought about his comments and now feel obliged to advance an argument in of the much-maligned inch.
Long, long ago, in my wild and reckless youth, I too was a champion of the metric cause. And it still seems reasonable that measures of volume and weight could be simplified by adherence to that system. When it comes to the centimeter, however, I must depart from conventional wisdom and declare the inch to be the superior unit.
To start with, the centimeter is simply too short. It can only be divided into ten easily visible increments, or twenty barely visible ones— and twentieths, or half-millimeters, are as fine as any metric measuring device shows. The inch can be divided into sixteenths, which are quite easily seen, and into thirty-seconds, which are bigger than half-millimeters. I won't even deal with sixty-fourths, which are too fine for my "mature" vision but which do appear on most good measuring devices.
All measuring systems are based on arbitrary standards. The meter is one ten-millionth of the length of a quadrant of the meridian. And the standard, which is nearly that, is kept in Paris. The foot is, as one would imagine, based on the average length of a human foot and seems to me to be somewhat more user-friendly.
The fact that the metric system is based on 10, or decimals, is what its defenders find most attractive. And they are correct: In most cases, decimals are easy to manipulate. But in the woodworking world, decimals present a big problem.
The most common calculation in woodworking is division by two. We always need to find the center of a rail, a stile or an edge. The common foot with its 12 inches can be divided by two into
6, 3. 1 V2, ty. 3/g, 3/k>> 3/32, 3/64. The meter, meanwhile, divides by two into 50 cm, 25 cm, 12.5 cm, 6.25 cm, 3.125 cm—and this is where the metric scale runs out of increments, because there are no marks finer than 0.5 mm. So, the foot can be halved eight times, while the much longer meter can only be halved four times.
Let's suppose you have a 3^-in. board. You want to lay out a tenon whose thickness is half the board's, with each shoulder one-quarter the thickness of the board. Instead of -Vj^ - -Vg -Vjg in., you'd need to measure 4.75 mm - 9.5 mm -4.75 mm. Bear in mind that 0.75 mm does not appear on a metric scale—you have to interpolate it. Any metric measurement with an uneven number will quickly pose problems for the woodworker.
If the metric system ruled, there is little doubt that lumber manufacturers would soon reduce standard lumber thickness to 18 mm, which would lessen the problem a bit—half of 9 is 4.5, andhalf oi 4.5 is 2.25—but we would still be faced with those difficult decimals that extend beyond tenths.
Naturally, those who have grown uj with the decimal system will be resistant to change—just as English-system user? already are. I expect that the metric system will eventually become standarc throughout the world. Still, I count mj blessings for having learned my fractions. Woodworking would be more difficult without them. A
J. R. Beall is a professional woodworker and too/maker in Ohio.
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