Abstract: The intermediate devices for digital instrument standards are introduced. Suggestions on how, when and how frequent to carry out intermediate checks, how to record and process the check results are analyzed. A method of comparison between instruments of same level is proposed as an effective way to show the stability of digital instruments standards by setting up control charts of DC voltage, AC voltage and AC current based on analyses of the process datum acquired from intermediate checks.

Key words: Digital instruments, Intermediate checks, Process parameter, Control chart