In message , "Dave Plowman (News)"
wrote


I've got some ways of calibrating DVMs,

While you may have some accurate ways of calibrating (or checking the
calibration of) a multi-meter I guess the average electrician doesn't.
Was that resistance measurement really 2 ohms or was it actually 4 ohms
but with a partially fried ranging component?

and they don't drift that much -
if well made.

If not subjected to (accidental) abuse the underlying DVM part of the
equipment may not drift that much in a well made piece of modern
equipment. Any form of accidental abuse may outwardly give an indication
that no damage has been done because the meter still gives a reading but
one or more of the ranges may be widely inaccurate. How many
electricians are proclaiming installations are safe and are writing
certificates while still using equipment that has never been checked for
accuracy since they purchased it.

In some ways, calibration is a bit like CORGI etc
membership. Just to satisfy the suits.

In some respects yes, if taken to the extreme , but also regard a
regular calibration in the same way a road vehicle MOT test. Many faults
are not identified until someone else checks out the equipment.

--
Alan