Calipers are simple instruments, but small habits separate a reading you can trust from one that's quietly wrong by a couple thousandths.
Zero before you trust it
Close the jaws fully and confirm zero (or re-zero a digital caliper) before each use, and periodically during a job — drift happens, especially with a low battery.
Measure square, not at an angle
The jaws must be perpendicular to the surface being measured. A caliper held at even a slight angle reads long — the most common source of caliper error on the shop floor.
Don't clamp it like a vise
Calipers measure with a light, consistent contact force — squeezing the jaws hard enough to flex a thin or soft part gives a falsely small reading. Let the jaws contact; don't crank them down.
Clean the jaws and the part
Chips, oil film, and coolant residue between the jaws and the part are invisible thousandths of error. Wipe both before a critical measurement.
Know its real resolution
A caliper that displays 0.0005" isn't necessarily accurate to 0.0005" — typical caliper accuracy is ±0.001" to ±0.002" depending on quality and length. For tighter tolerances, step up to a micrometer or gauge block comparison.