Caliper hole distance adapter for Plastic Caliper

Description straight from Royce's original publish:

This is a little helper to properly measure hole distances.

Put two of the cones on the tips of your caliper and slide together.
If your value is bigger than 20mm, note that down and substract that overhead from your measured value.
Example:
My overhead is 0.9mm
Measured distance - 0.9mm = real distance

Minimum distance to measure is 20mm obviously