The silent error
Zero error
Close the jaws completely. The vernier zero should sit exactly on the main scale zero. When it does not, the instrument has a zero error, and it will add itself to every single reading you take until you correct for it.
What makes it dangerous is that it is invisible in the results. A dropped or worn caliper does not produce obviously wrong numbers; it produces plausible numbers that are all wrong by the same amount. Nothing in a batch stands out as anomalous, so nothing prompts you to check.
Positive error
Vernier zero sits to the right.
The scale reads high. Subtract the error from every reading.
Negative error
Vernier zero sits to the left.
The scale reads low. Add the correction to every reading.
Switch the zero error control in the simulator to +0.04 mm and take a measurement. The jaws stop in exactly the same place as before — the part has not moved — but the scale now reads 0.04 mm high. That is the whole mechanism.
Try it
Everything on this page is easier to believe with the instrument in front of you.
The simulator has draggable jaws, three least counts, imperial mode, zero-error simulation and a practice mode that marks your readings.
Open the caliper simulatorKeep reading
How to read a vernier caliper
The five steps, the TR = MSR + (VSR × LC) formula worked through, and the six mistakes that spoil a reading.
Least count
Where 0.02 mm comes from, a table of every common vernier, and the four jobs a caliper is the wrong instrument for.
Parts of a vernier caliper
All twelve parts named and explained, plus the ISO, ASME, BS and DIN standards that govern them.
Frequently asked questions
Short answers to the questions that come up most often about reading and using a caliper.