Draft Document – Geometrical product specifications (GPS) – Micrometers – Part 1: Micrometers for external measurements; Limits for error
standard by Deutsches Institut Fur Normung E.V. (German National Standard), 11/01/2009

Draft Document – Geometrical product specifications (GPS) – Micrometers – Part 1: Micrometers for external measurements; maximum permissible errors
standard by Deutsches Institut Fur Normung E.V. (German National Standard), 07/01/2016