This is an addendum to my previous post -
After some thought I’m inclined to the conclusion that Critical Limits as nominally stated assume calibrated instruments, ie are to be used with "calibrated data".
Referring to the thermometer in this thread, both the factors (-0.3 and +/- 0.49) are related to the thermometer, so that an indicated value of 140.6 degC is best expressed as a (calibrated) result something like –
The “true value” is 140.3 +/- 0.49 degC with 95% confidence
In a process scenario as applicable to BRC 6.4.3, it is regarded as necessary to assume a worst case scenario related to the (permanent) factor 0.49 which is compensated for by increasing the theoretical critical limit of, say, 140degC to a minimum of 140.49degC. (as per Izzy/Tony).
Assuming the use of calibrated data the Critical Limit would then be a minimum of 140.49 degC
However in practice for a dedicated thermometer/machine, IMEX machine operators prefer to act as per the thermometer’s indicated value which would necessitate an action limit of 140.79 degC (as per Tony’s formula). (digital offsets / re-settable analog units would also work if available)
Again, if the thermometer is in general random use, IMEX a calibration correction factor as appropriate to the application (cf. -0.3) is simply, directly noted on the instrument. For some usages the uncertainty factor IMEX is undoubtedly simply (wrongly ?) ignored.
So IMO the preferred action regarding factor -0.3 depends on the situation. Either way, it’s used.
Plus one certain thing from BRC’s POV (6.4.3) is that the uncertainty factor +/- 0.49 must be used.
So IMO the answer to post 16 is regretfully No.
PS - texts suggest that the quoted uncertainty factor is derived within a lab's highly controlled environment and that values in practical situations can be substantially higher.
PPS - this is not a simple subject.