A method, including inserting a probe into a cavity ina subject's body and receiving, from a force sensor in theprobe, first readings indicative of a first change inmeasured contact forces between the probe and the cavity byless than a predetermined limit over at least apredetermined interval of time. The method continues byreceiving second readings from the force sensor when thesecond readings have changed by more than a predeterminedforce threshold or location coordinates of the probe havechanged by at least a predetermined location changethreshold. The method continues by receiving third readingsindicative of a second change in the measured contactforces between the probe and the cavity by less than thepredetermined limit over at least the predeterminedinterval of time. The method concludes by calibrating azero-force point for the force sensor according to thethird readings.
