How do I read a 0.02 mm vernier caliper?

Whole millimetres from the main scale left of the vernier zero, plus the number of the vernier line that lines up × 0.02 mm. Example: 40 + 13 × 0.02 = 40.26 mm.

Why does a tilted caliper read too large?

Tilted along the part axis, the jaws span an ellipse that is wider than the diameter; the error grows with the angle (L / cos α).

How to Read and Use a Caliper — Vernier, Dial and Digital

Parts of a caliper

A caliper has a beam with the main scale and a fixed jaw, and a slider (frame) that carries the moving jaw and the reading device: a vernier plate, a dial or a digital display.

The large lower jaws are the outside jaws for shafts and other outside sizes. The small upper jaws are the inside jaws for bores and slots. The depth rod runs out of the end of the beam as the jaws open, for depths and steps. The lock screw on top clamps the slider; the thumb rest or thumbwheel moves it.

How to read a vernier caliper (0.02 mm)

On a 0.02 mm vernier caliper the vernier plate carries 50 divisions spread over 49 mm, so each vernier division is 0.98 mm — 0.02 mm shorter than a main-scale millimetre.

Read the whole millimetres on the main scale just to the left of the vernier zero line.
Find the one vernier line that lines up exactly with a main-scale line.
Multiply its number by 0.02 mm and add it to the millimetres.

Example: the vernier zero is just past 40 on the main scale and the 13th vernier line lines up: 40 + 13 × 0.02 = 40.26 mm. The labels 0–9 on the vernier mark every fifth line (0.1 mm steps).

Look straight at the scales. Seen at an angle the vernier lines appear shifted (parallax) and you can read the wrong line. In KELIBRON the “face the readout” view turns the camera square to the scales.

How to read a dial caliper (0.01 mm)

A dial caliper shows whole millimetres on the beam scale and hundredths on the dial: one revolution of the needle is 1 mm, divided into 100 divisions of 0.01 mm.

Example: the slider edge is past 28 mm on the beam and the needle points at 3: 28 + 3 × 0.01 = 28.03 mm. Before measuring, close the jaws and turn the bezel so that 0 sits under the needle, then lock the bezel.

How to use a digital caliper

A digital caliper shows the value directly, typically to 0.01 mm. With the jaws closed press ORIGIN to set the absolute zero. ZERO/ABS sets a relative zero anywhere (INC mode, for comparing to a master) and switches back to absolute (on many models by pressing and holding). UNIT switches mm / inch and HOLD freezes the reading.

Measuring an outside diameter

Check the zero with the jaws closed.
Open the jaws a little wider than the part.
Put the part deep in the jaws, close to the beam (less Abbe error), with the beam square to the part axis.
Close the jaws gently with light, even force until both faces touch; read the value.

Measuring an inside diameter (bore)

Close the jaws to a little less than the bore and put the inside jaws into it.
Open the jaws until both blades touch the wall.
Keep them on the diameter: rock gently across the bore for the largest reading, and along the bore axis for the smallest.
Read the value.

Measuring a depth

Stand the caliper upright and rest the end of the beam flat on the reference face (the open face of the hole).
Hold the beam end down and push the depth rod out until it touches the bottom.
Keep the beam square to the face, then read the value.

Checking the zero

Before every series of measurements, take the caliper off the part, wipe the faces and close the jaws (the depth rod draws in flush). The reading must be 0.00. On a digital caliper press ORIGIN; on a dial caliper turn the bezel to zero. A vernier caliper cannot be re-zeroed: note its zero error and subtract it from every reading.

Common wrong use and how to correct it

Task	Wrong use	Effect on the reading	Correction
Outside	Caliper tilted along the part axis	Too large (the jaws span an ellipse)	Keep the beam square to the axis
Outside	Zero not checked	Off by the zero error	Close the jaws and set the zero first
Outside	Chip or dirt on a jaw face	Too large	Wipe the faces and the part
Outside	Too much measuring force	Too small (the jaws spring)	Close with light, even force
Inside	Blades off the bore’s diameter	Too small (a chord)	Rock across the bore for the largest reading
Inside	Tilted along the bore axis	Too large (D / cos α)	Square to the axis; rock along it for the smallest reading
Inside	Chip on a blade edge	Too small	Wipe the blades and the bore
Depth	Beam end not resting on the face	Too large by the gap	Hold the beam end down first
Depth	Caliper not square to the face	Too large (h / cos α)	Keep the beam perpendicular, whole end face down
Depth	Chip on the bottom of the hole	Too small	Clean the hole and the rod tip

Judging a part against its tolerance

A drawing size such as Ø20 0/−0.05 gives the limits 19.95 mm and 20.00 mm. A part passes when the reading lies within the limits and fails low or high outside them. A reading taken with a wrong setup (tilt, unchecked zero, debris, too much force) must never be accepted — KELIBRON does not judge such readings at all.

KELIBRON is a teaching simulation: it is not a calibrated instrument and its readings are not certified measurement results.