Dear Mr. Wayne,
Thanks for this interesting topic. To be honest, I am not able to take position as I feel both for and counter points are right in their own perspective.
Yes, I do agree that there is no guarantee that the calibration is valid after it leaves the lab and so, the relevance of expiry date is gone. But, I also agree that the expiry dates should be specified on both certificate and equipment as it indicates to the user about the risks involved when the equipment is nearer to re-calibration/ re-inspection.
When we agree that the calibration due date is not required on the certificate & equipment, in one way we are saying that the trust worthiness of that equipment is gone and we are not sure of the results of testing/ measurement. This is not a healthy sign and it results in blame game when process inspection indicates the non-conformance in the product.
Definitely, internal checks are required but one can not apply to all testing/ inspection/ measuring equipment. It should be on case to case basis and depending upon the use, kind and volume of production, the frequency of recalibration could be increased/ decreased.
If any error is detected during the recalibration and at-least we could initiate the corrective action immediately and minimize the damage to the product/ Company reputation and rectify the defective products as we can trace them by specifying the IMT equipment ID # on the quality record. Probably that might be the reason why ISO 9001:2000 Clause 7.6a requires recalibration at specified intervals.
I personally feel that the Quality personnel are best to judge the interval as they know the usage and importance of testing.
Rajeev