Often when using a demagnetizer in NDT, passing a megnetized rod, bearing race, shaft etc... we put D/C current through a part to mag it, then when the inspection was done, we passed the parts through an A/C coil field to demagnetize the parts. We verified this with a gauss meter which was calibrated.
I would apply some logic to this, if you are using a demagnetizer of some sort, then the device used (gauss meter) to verify the conformance of demagnetization, then only the device used to check demag should be calibrated in this case the gauss meter.
" Remanent magnetic fields can:
affect machining by causing cuttings to cling to a component.
interfere with electronic equipment such as a compass.
create a condition known as "arc blow" in the welding process. Arc blow may cause the weld arc to wonder or filler metal to be repelled from the weld.
cause abrasive particles to cling to bearing or faying surfaces and increase wear.