(as i understand your question is to deal with critical variables and its precision and accuracy)
in short and brief.....generally speaking...
process validation is not to do extra-additional measurement of critical variables. any efforts in ensuring the correctness-precision-accuracy of the critical variables is an pre-validation exercise. (PV is not challenge the precision and accuracy of an temperature probe or an timer!!!)
PV is mainly to do that extra&additional measurement of quality attributes, such that, the data demonstrates the confidence and reproducible of the process. in order to do that, we might draw additional samples for analysis of CQAs and analyze to generate required data.
now
in the context of quality by design, we tend to treat certain inprocess parameters as critical variables, in such case, it might be relevant, but i guess that is out of scope for now!!! (neither QbD and nor new-Process validation guideline have yet come into force...ie.., become an audit agenda etc., wrt regulatory enforcement...)
still, if that is what you are looking, for...then the ans is little different...
here are few quick discussions....but not focussed on overall new-PV guidance etc.,
Process Validation Protocol (API) as per new FDA Guidelines
Sampling Plans - Guidance to Sampling a Process during Validation
but here's where we look forward to hear little more specifics/examples to respond more precisely...
hope that it helps...