Micrometer zero check and zero error correction

Why the zero drifts

The measuring faces wear, and the frame responds to temperature and handling. A micrometer that read zero last week can sit a few divisions off today — so the zero check is part of every measurement, not an occasional chore. Standards: ISO 3611 internationally; in China GB/T 1216 (product standard) and JJG 21 (verification regulation).

The zero check, step by step

1. Wipe both measuring faces with a soft, lint-free paper.
2. 0–25 mm: turn the ratchet until the faces close and the ratchet slips — never screw the thimble down hard on the faces.
3. 25–50 mm and up: close gently on the setting standard supplied with the micrometer (25, 50 or 75 mm for the matching range).
4. Look at the reference line: the sleeve zero and the thimble zero must coincide.

Zero error: read it with its sign

The reading with the faces closed (or on the setting standard) is the zero error, positive or negative: closed and it reads +0.03 mm → zero error +0.03 mm; closed and it reads −0.02 mm → zero error −0.02 mm. On ranges above 0 the faces on the standard must read the standard’s size instead of 0.

Correcting every reading

True value = reading − zero error (zero error keeps its sign). Worked examples: zero error +0.03 mm, reading 24.87 mm → 24.87 − 0.03 = 24.84 mm. Zero error −0.02 mm, reading 10.14 mm → 10.14 − (−0.02) = 10.16 mm.

A small, stable zero error is workable — correct it in the record. A large or drifting one means the micrometer needs adjustment or service.

Adjusting a mechanical micrometer

Most micrometers carry a small spanner for the sleeve: close on zero, turn the sleeve until the zeros line up, then check again. Follow the maker’s instructions for your model, and re-check on a second closure — an adjustment that is not re-verified is a new error.

Digital micrometers: ORIGIN

A digital micrometer has no zero line to align: close the clean faces (or close on the setting standard for ranges above 0) and press ORIGIN (ZERO on some models); the display then reads zero, or the standard’s size on a larger range. Do this before each measuring session, and after any large temperature change.

The daily check is not a calibration

A zero check catches drift before it enters a reading; it does not replace periodic verification. In China, micrometers are verified per JJG 21《千分尺检定规程》; elsewhere follow the maker’s interval and your quality system, and keep the certificates in the gauge register.

In KELIBRON

The mechanical micrometer scenes open with a zero beat: scene-micrometer-reading closes a 0–25 mm micrometer on itself and must read 0; scene-micrometer-zero-50 closes a 25–50 mm micrometer on its 25 mm setting standard and must read 25.

On a digital range above 0, scene-micrometer-digital-50 sets zero with ORIGIN on the same standard. Open the scenes and watch the readout while the faces close.