No anomalous scaling in electrostatic calibrations for Casimir force measurements

In a recent paper [Phys. Rev. A 78, 020101(R) (2008)], Kim have reported a large anomaly in the scaling law of the electrostatic interaction between a sphere and a plate, which was observed during the calibration of their Casimir force setup. Here we experimentally demonstrate that this behavior is not universal. Electrostatic calibrations obtained with our setup follow the scaling law expected from elementary electrostatic arguments, even when the electrostatic voltage that one must apply to minimize the force (typically ascribed to contact potentials) depends on the separation between the surfaces.