What is your calibration interval for frequently used measuring tools?
Even the digitals have mechanical components that can wear and need "adjustment".
What checks do you perform when accurate (not relative) measurements are needed?
Zero is pretty easy, but what about 3.875"? Gear lash in dial, skipped pulses in digital.
Is it the same as a couple years ago, before you dropped it?
Has your "Standard bullet, case, cartridge changed length over the years?
I know, I'm always harping on a meaningful (near your target) check standard.