I agree with the quantitative aspects of yr comments, and the reality check. The intrinsic problem may be additionally with BRC semantics ?.
Personally I have yet to find any “guaranteed” machine sensitivity (in the sense of a meter reading) for purchased MDs, or for the "calibration" check wands for that matter (equally [negligently?] I hv never asked for such specifics either ). My only agreed purchase "sensitivity" specification was for the unit to "visibly" detect/reject a certain "Xmm" wand, information as to which is typically given in brochures. People with better (non-anecdotal) knowledge than myself regarding what may be available are only too welcome to add it to this thread.
Previous threads hv discussed these issues and seem to mainly indicate absence of “hard” quantitative data ( choosing representative / reproducible test conditions is presumably one tricky factor). Typical magnetic strengths (gauss readings) have been mentioned as one possible criterion. For most people this would probably would require external assistance.
IMEX, external service technicians are also reticent over the validation of their own numerical MD “calibration” procedures also (eg “supplied” by the manufacturer). The recipient (beleaguered QA Mngr) of the conforming piece of paper is usually unconcerned about such niceties unless they are considering to take-over the job themselves.
I did note that no specific mention of “external” or "calibration" appears in the BRC, MD-specific text 4.10.3 (although the latter word is an implied requirement as per sec.6.3).
Sadly, I would also add that for some, less-enlightened companies, money questions for external calibrations can also surface unless specific QA justifications are supplied. This is the “senior management commitment” issue again.
One obvious query is as to what BRC themselves (ie auditors) expect by the standard’s use of “sensitivity”. ?
My own auditorial experience has been that “sensitivity” is interpreted as a visible +/- rejection action for the specified/certified "Xmm" check wand as per my original documenteded procedure ( any failure would clearly have routine CCP implications). Others may hv different experiences of course. Specific BRC auditorial non-acceptance of a visual criterion would certainly be interesting to hear about ?
Rgds / Charles.C
PS - again on semantics, i find the slight wording variations between bullets 2,3,4 of para 188.8.131.52 (and also when combined with para.184.108.40.206) rather suggestive/suspicious but only BRC (and the auditors?) know the whole story. So far.
PPS - as an example only, here is the Tesco (2009) viewpoint on "sensitivity" (eg para 220.127.116.11) -
COP for Metal Detection&X ray Systems.doc 630KB
P3S - just noticed the OP did not refer to any particular standard but i guess the posts are fairly generic, at least as far as sensitivity is concerned. SQF's specific requirements for a MD, if any, no idea. But may be relevant, and equally obscure .