  Kelvin probe force microscopy at normal pressure was performed by two
different groups on the same Au-coated planar sample used to measure the
Casimir interaction in a sphere-plane geometry. The obtained voltage
distribution was used to calculate the separation dependence of the
electrostatic pressure $P_{\rm res}(D)$ in the configuration of the Casimir
experiments. In the calculation it was assumed that the potential distribution
in the sphere has the same statistical properties as the measured one, and that
there are no correlation effects on the potential distributions due to the
presence of the other surface. Within this framework, and assuming that the
potential distribution does not vary significantly at low pressure, the
calculated $P_{\rm res}(D)$ does not explain the magnitude or the separation
dependence of the difference $\Delta P (D)$ between the measured Casimir
pressure and the one calculated using a Drude model for the electromagnetic
response of Au.
