Techniques have been developed to measure resistances from 10−7 to over 1014 Ω. Needless
to say, at the extreme ends of this range, specialized instruments must be used. We have
already seen in Chapter 4 that very accurate resistance measurements are commonly made
using DC Wheatstone or Kelvin bridges and a DC null detector such as an electronic nanovoltmeter.
The values of the resistances used in these bridges’ arms must, of course, be
known very accurately. In the following texts, we shall discuss other DC means of measuring
resistance.