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In a scanning force microscopy (SFM, or atomic force microscopy) system, a simultaneous recording of the probe cantilever deflection and the corresponding probe-sample distance yields a so-called force-distance curve. When the SFM probe is away from the sample surface, there is no significant interaction between the probe and the sample and hence the deflection angle is constant. This results in a zero force change in the force-distance curve. However, in SFM probe-scanning geometry as opposed to sample scanning, a nonzero force change in a force-distance curve before probe-sample contact is usually observed. This article discusses the reasons for this phenomenon and its implications for contact mode SFM imaging and complementary measurements. It is found that such a slope is directly related to the minimum probe-sample contact force and the force uniformity that the microscope can achieve during contact imaging. Possible solutions, including a “variable set-point” scheme, are proposed. © 1997 American Institute of Physics.