01
Convert but keep the original dimension
One inch equals 25.4 millimeters. Record both systems and identify which controls. Rounding a dimension for a sales description should not silently change the exposure calculation.
02
Check thickness separately
Nominal 5, 6, 7 or 9 millimeter products each have their own tolerances. Convert the specified range, not only the marketing label, when selecting fasteners and assessing weight.
03
Measure hole location in the same system
Punch position, headlap and exposure interact. Mixing rounded inches for one measurement and exact millimeters for another can produce cumulative layout error.