I would agree about the 1/8ths, those increments are of very little value indeed. If you look at datasheet sheets for component pad sizes they quote metric and inches in 1/10ths. Dont ever recall seeing a pad size dimension along the lines of 3/64ths x 1/8th.
What would be very useful is to have one one edge a measure of the number of pins on a header strip, a count that starts at one. Yes I know a 32 pin 0.1" header would be 3.1" between the pins, but a rule marked 1 to 32 would make it much easier to cut header strips to length.
Other common sizes for measuring header strips would be spacings of 2mm, 1.5mm, 0.05" etc.
it would also be good if 0 on cm and inch rules started at the actual end edge of the the ruler and not 1mm from the end.
Add some text on the ruler with common metric imperial conversions, mm to inches, grams to ounces etc.