What can disturb the measurement of high value resistors (1 gigaohm and above)?

The measurement of high-value resistors, particularly those rated at 1 gigaohm and above, can be significantly affected by the conductivity of insulating materials. When measuring such high resistances, the insulation around the resistor and in the measurement circuit can become a considerable factor. If the insulating materials are not perfectly non-conductive, they can introduce unwanted paths for current flow, thereby affecting the total resistance measured. This is particularly crucial because high-value resistors have very low leakage currents, which makes them highly susceptible to any external conductive influences.

When insulating materials have even slight conductivity, their effect can overshadow the intended measurement, leading to inaccurate readings. Therefore, it's essential to ensure that the materials used in the test setup, including test leads and connections, are appropriate for the high resistance being measured to ensure the reliability and accuracy of the results.