This guide covers the use of callipers and micrometers for internal, external and depth measurements. The issues covered include the effect of measurement force, both when a ratchet is present (e.g. micrometers) and when it is not, particularly when measuring soft materials; use and general care, support and handling of micrometers and callipers; guidance on choosing the most appropriate equipment type for the measurement; advice on calibration and verification methods and how to generate an uncertainty budget for a measurement; use of electronic instruments, fault awareness, temperature effects; awareness of errors introduced into internal knife edge jaws as external/internal jaws wear; and standard calibration methods and reporting of results.