 When the distance is changed but "ΔV"sp is held constant, a current will flow due to the change in capacitance.This current is proportional to the vacuum electric field, and so when the electric field is neutralized no current will flow.Although the Kelvin probe technique only measures a work function difference, it is possible to obtain an absolute work function by first calibrating the probe against a reference material (with known work function) and then using the same probe to measure a desired sample.