There is a debate about the recalibration date, we perform our plan on monthly basis & the auditor insists to be done by day, so the calibration validity ends by the cal. month 1st.date. which method is more accurate?
How often you perform external or internal calibrations and whether you need to perform intermediate checks (verifications), and how often; depends on the process steps and what equipment is used. No auditor can dictate the period or specific day when calibrations and verification must take place, unless there is a requirement in your proceure, in the method or from a regulatory body. For example, for analytical balances it is straight forward – a laboratory would use a set of weights that they own, where each piece has metrological traceability to SI, where they were previously calibrated by an external calibration provider (at a suitable frequency, based on risk and need). So here you have reported uncertainties on the calibration certificate that you confirm are acceptable for each piece. Then you perform intermediate checks (verifications) on your balances at suitable time intervals (also based on risk), across the range of use (g) of the balance. For balance, this is typically daily.
For further information have a look at the ILAC G24:2007 Guidelines for the determination of calibration intervals of measuring instruments (note currently under revision) available for download at https://ilac.org/?ddownload=818