This standard BS 6468:2008 Specification for depth micrometers is classified in these ICS categories:
17.040.30 Measuring instruments
This British Standard specifies requirements for spindle type S and rod type R depth micrometers with a micrometer traverse of 25 mm or 1 in, covering measuring capacities from 0 to 300 mm, or 1 in to 12 in.
Annex A gives methods of test. Advice on use is given in Annex B.