Re: IATF 16949 Cl. 7.1.5.1 - Documented information as evidence of fitness for purpos
Sometimes going one section forth or one section back is helpful.
You are referring to plain ISO requirement, where we (I mean automotive) have own more detailed requirement - 7.1.5.1.1. There is an answer to your question. Fit for purpose is evidence, that it makes sense to use this monitoring resource, as it was confirmed through measurement system analysis.
Fit for purpose is one step further than calibration activities. We already know, that after calibration, this monitoring resource used by competent person (e.g. us) gives valid results, but what about other people. Maybe they are not competent enough, maybe not consistent enough and then we would be forced to switch to other monitoring resource.