Can anyone please tell me where the laid down standard is for calibrating ESD wristband testers. I understand it's 3 monthly although a colleague says it's an annual requirement.

If there is no statutory requirement to calibrate a piece of test equipment, then the best approach is usually to follow the manufacturers recommendations.

If there are no recommendations then you have to look at the combination of the consequences of the equipment failing and the likelihood of a failure. If you find a failure then you should shorten the test interval.

Generally with ESD wrist straps you are not looking at an accurate measurement (more of a go/no-go), So you could also consider creating a little test jig with some resistors and a switch, or just test wires with resistors, this would enable you to test the tester at any time. (For traceability you could test the resistors with a calibrated meter and log the information in the calibration log)

Hope that helps..