Measurers often seem to calculate the % difference between two counts by first converting them to the equivalents in standard units of length. (Farcically I have seen some of these lengths expressed down to one thousandth of a mm!)
These conversions are unnecessary because the % dfference can be more easily calculated directly from the counts themselves. This is particularly easy on HP calculators with RPN where only the counts are entered and the % change button pressed:
C1, enter, C2, shift %chg
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