When measuring insulation resistance R60, it is possible to use measured values to determine other values R1, R2, C2 that are characterised by a picture of an equivalent circuit of insulation.

To do this, it is necessary to record four readings during measuring within 15, 30, 45 and 60 seconds (R₁₅, R₃₀, R₄₅, R₆₀). These values are then filled in a table on web pages http://www.eldiag.cz/vypocet-izolace.php where you can determine values of up to three sets of measurements at the same time.

Conditions for calculation are increasing time values, internal resistance of a measuring device smaller than the measured resistance and good precision of reading.