write a lookup table for the common sizes.
think the greek letter Π comes into the equation.
got one of them but it's in english. 1/1000th inch divs.https://www.amazon.co.uk/Metric-Out...=1511897929&sr=8-5&keywords=metric+micrometer
Brilliant device, and accurate.
So conversion to metric size after finding CSA then for you...got one