The simplest method, in a nutshell, is don't over document the requirements. If you are only calibrating calipers, the scope of the lab should be quite simple. I would guess that you may perhaps even be able to write one spec to cover the entire process if indeed the lab scope is that small.
If you are calibrating in house, and the calipers have an impact on product quality, reliability, etc., then you will need to document. In situations such as that, I have seen some companies make the decision to go to an outside contractor just to avoid the details they need to cover for compliance. I am not suggesting that, as there are certain added risks which will most certainly ensue. When you go to a subcontractor, you automatically lose a degree of confidence and control over the quality of those calibrations. But that is a decision that must be locally decided. I don't want to be construed as recommending which course of action will be better in your circumstance. Simply that you'll need to weigh out the risks versus the cost and confidence level, etc.
To do it in house, you'll need an adequate written procedure for how to calibrate the calipers, the right standards, the right environmental controls, appropriate training, and the other details, and have the system documented.
After that mouth full, it must certainly be added to reiterate above, that you don't need to make it any more complicated that necessary.
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