[trobbins]

Measurement accuracy will always come down to whatever meters are available for setup, and in addition whether there is a meter with an accurate current measurement, or the alternative of a meter with an accurate voltage measurement and known precision resistor.

Almost nobody would have a calibrated meter unless they just purchased a meter, or had meters at work that were annually calibrated - so the outcome for most of us is what confidence we have in the meters we have.

That's one advantage of buying a cheap new 4-digit handheld meter like the ANENG 8009 or similar, as they can provide reasonable mV measurement accuracy - so for example a sample 0.33 ohm 5% 3W emitter ballast resistor shows a 3.186mVdc meter reading with my 10mAdc 317L CCS using 4-point connection scheme. That reading varies 0.04 mVdc when the 4-point clips move the voltage points from next to the resistor body out towards the ends of the resistor terminal wires (where the current clips are).