Insulation testers are designed to measure at the opposite end of the resistance by inserting high DC Voltage. Insulation testers use high test voltages in the kilovolt range. The area between electrode and ground is charged with high DC Voltage and we do not want grounds that measure in megohms. Ground testers use Low Voltage for testing for operator safety, to low voltages.

However, a Multimeter or continuity test can use very low Voltage between an installed electrode and a reference ground, which is assumed to have negligible. Low voltage DC can produce a resistance reading between ground and an earth electrode but it is not an accurate measurement. Multimeter measurement may not be reliable, since reading can be influenced by soil transients, the electrical noise that is generated by utility ground currents trying to get back to the transformer, as well as other sources.