A scanning probe microscope comprising: a signal generator providing a drive signal for an actuator to move a probe repeatedly towards and away from a sample. In response to the detection of an interaction of the probe with the sample the drive signal is modified to cause the probe to move away from the sample. The drive signal comprises an approach phase in which an intensity of the drive signal increases to a maximum value; and a retract phase in which the intensity of the drive signal reduces from the maximum value to a minimum value in response to the detection of the surface position. The intensity of the drive signal is held at the minimum value during the retract phase and then increased at the end of the retract phase. The duration of the retract phase is dependent on the maximum value in the approach phase.