4. Other measurement procedures or preservation standards

Connection and conservation standards, as well as the zeroing methods just described, can be used to measure DC resistances or voltages, with uncertainties of a few millionths.

For much smaller uncertainties (a few 10 ^–9 : case of national metrology laboratories), the conservation standards described are no longer usable.

Conversely, when the desired uncertainties are much greater (a few 10 ^–4 or more: this is the case for most industrial measurements), the methods described above are too cumbersome to use, and involve equipment that is often too expensive.

For these two extreme cases, and by way of illustration, a few brief details are given below.