Operational Units vs. SI

OK, so maybe that’s a provocative title for strict adherents to the SI system of units, but we are going out on a limb here.   The SI makes it clear that its official set of units are really the only ones we ought to be using.   13 units are named as outsiders that are OK in a pinch, and another 11 listed that are “under consideration”, but feet and inches? Sorry.   Not even under consideration.  In the SI’s defense, these are not entirely matters of dogma or bureaucracy; SI’s rules are carefully constructed to support the most precise representation, and for keeping a firm repeatable basis for measurement.  So we agree that SI is a great piece of work and absolutely should underpin all measurement.  

Where we take issue is this: now that computers are our desktops and tools, we no longer need to directly use the SI system whenever we measure something.   When an American machinist gauges a part, he certainly will use a micrometer that is calibrated in inches.  If he writes down 3.022″, we understand that this is measured to the accuracy of that micrometer. Converting this to SI, we end up with 0.0767588 m which appears to be a more accurate measurement.  If diligent, we would present the result rounded to a precision similar to that of the original measurement, but you get the idea:  something is lost in the translation. 

Physics, the world we live in, and the tools we use, measure things in units appropriate to the situation, and we believe that such measurements are primary data that should not be lost.   In our view, the SI should, like the floating point standard inside our computers, be the gold standard for measurement, but not its only expression.  In that spirit, truenumbers  preserve whatever units of measure a number is originally expressed in, as well as its SI representation.  We can think of this approach to units as operational, because it supports the operations performed by technical people, using the SI as means for accurate internal representation.

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