I received my Master of Science degree from RPI in 1977.  What was the most interesting thing I learned, you ask?  The dirty little truth of the metric system.

Hey, units of measure have been a problem right from the start.  It got so bad at one point that standards for units of measure were spelled out in the Magna Carta!  Go look…it’s true.

The problem was taxes.  One year the king wanted higher taxes, but instead of raising the number of bushels a farmer owed, the king simply changed the size of an official bushel.  So, when they forced the king to agree to the Magna Carta, they included standardized units of measure in the document.  That worked until King Charles I started ignoring the Magna Carta.  And from that came rhymes like, “Jack and Jill went up the hill to fetch a pail of water…”  At the time, Jack, Jill, and pail were all units of measure.  The rhyme goes on to say that “Jack fell down, ” referring to a change in the size of a Jack.  “And broke his crown” referred to the king.

And then there was another rhyme, “A pint’s a pound the world around.” Where did that come from?  Well, according to our Heat Transfer professor, who once spent a whole class period decrying the metric system, it was part of a union protest song against the incorporation of the metric system.  As you are aware, pints and pounds do not belong to the metric system.

So, what’s the big deal?  Why don’t we just change to the metric system and have done with it?  And here is where it gets interesting.  The primary reason why we in the United States stay with the English system of units is…you waiting for this?…screw threads!  There is no equivalency between metric thread sizes and English thread sizes.  The cost to manufacturers to make the change over in thread sizes, not only for their products, but also their machines, their instrumentation, their drawings, their documents, their tolerance studies, their stress analyses, their product literature, their stock of replacement parts,  the number of screws used in their parts, the number and type of screws stockpiled for new and replacement products, and the product literature for customers and customer service people would cost huge amounts of both time and money.  Guess who would pay for that…YOU!

And what is truly laughable about it is that few, if any countries are running completely on the metric system.

So here is another little thing you may not know.  Calories are not in the metric system.  For all intents and purposes, calories don’t exist.  I can’t wait to tell all the weight loss gurus that it is Joules, not calories, that are the units of energy recognized by the metric system.

Another well known secret that we aerospace engineers try not to tell anyone is that all length dimensions on airplanes and spacecraft are recorded in inches and decimals of inches.  We don’t use feet.  We don’t use yards.  Try to find anything but inches on our drawings or in our calculations?  Lots of luck!  I wonder how far it is to the sun in inches.  Somewhere around 5.9 trillion inches I believe.  No wonder it takes so long to get there.

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