How to Calibrate an External Micrometer - Moore and Wright
A setting bar and adjusting spanner will be needed to calibrate the micrometer.
The micrometer sleeve has a zero index line and scale, and a scale around the thimble.
To calibrate, get both the index zero and thimble zero to align.
Insert the setting bar between the measuring faces. Gently turn the thimble until you feel the ratchet click.
Locate the spanner with the hole in the back of the sleeve, and gently turn the sleeve until the sleeve index and thimble zero are aligned.
The Micrometer is now calibrated.