Thanks. Jim
That was the hidden thrust of my question. In effort to avoid this exact error, my new mob has come up with the idea of inserting QNH in the PERF APP page and using it as some sort of gross error check at transition. That is, not before...
Only, by that stage, it's likely going to be the same (misheard) QNH and won't alert a ship-coherent mis-set, anyway. In other words, if the (erroneous) source is the same, the error won't be trapped. And, at transition, it's too late anyways.
That's why QNH readback at altitude assignment is now a thing: it wasn't when I started a very long time ago - at least, not in my neck of the woods. Whenever you transition to QNH, then the setting needs to be verified by readback, or by reference to latest METAR or ACARS or similar data - but not from what you or Bloggs has inputted in the box.
If readback procedures are failing, then that's a whole safety of air navigation problem - not just an altimeter problem - and it needs to be addressed with requisite vigour, rather than by imposition of SOP 'band-aids'.
Cheers and thanks everyone, so far...
Last edited by Friendly Pelican; 11th Jul 2021 at 11:27.