If you own electronic calipers that have the feature of being able to be zeroed at any point, here's a clever use of that feature. Let's say you want to measure the center-to-center distance between two equal diameter holes. Use the inside measurement capability to measure the ID of one of the holes. Zero the calipers at this setting. In effect, you've now stored the negative of the diameter of the hole(s) in the caliper's measurement memory. Now use the inside measurement capability to measure across the outer edges of the two holes. Whatever is displayed on the calipers is the center-to-center distance between the two holes - the diameter of the hole(s) has been subtracted out for you automatically. The same trick works if the two holes are replaced by two equal diameter pins and you use the od measurement capability of the calipers.
If you need the center-to-center distance between two *unequal* diameter pins, measure the distance across them and the distance between them. The average of the two readings is the center-to-center distance. Works for holes too.
