Calipers are for making
quick and close measurements. All you can do with a caliper is clean and close the jaws, and then see if it "zeroes" when closed. If you need to make
precise or
critical measurements, then you need to own a
micrometer.
Calipers are handy and fast. You can get Inside, Outside and Depth readings really fast. And you can do "tricks" like "zeroing" a digital caliper at the perfect dimension, then all the items you measure will show how far they are (plus or minus) from "perfect".
And those answers will be good enough for most reloading needs. But do NOT equate "fast and easy" with "precise". Just because a digital caliper shows a number on the digital readout don't make it so. Especially when you are seeking answers at or smaller than 0.001".
Also note that a digital caliper is actually reading a small strip of magnetic recording tape buried in the caliper's handle. A "head" (very similar to those found in a cassette tape player) reads the increments recorded on the tape as they pass under the head. That's why digital calipers are only available in non-magnetic plastic or stainless.
IF the caliper is placed near strong magnetic fields, then, just like a VCR or audio cassette, the tape can be erased, thereby ruining the instrument's accuracy.
