Apparatus, comprising: a first probe configured to be inserted into a cavity in a body of a subject; a force sensor located within the first probe; a second probe configured to be inserted into the cavity in proximity to the first probe; and a processor, configured to: identify a first period wherein first readings received by the processor from the force sensor are indicative of a first change in measured contact forces between the first probe and the cavity by less than a predetermined limit over at least a predetermined interval of time, and first signals received by the processor are indicative of a first change in a measured value of the proximity by less than a predetermined proximity change threshold; identify a second period after the first period, wherein second readings received by the processor from the force sensor indicate that one condition is met from a set of conditions consisting of: the second readings having changed by more than a predetermined force threshold in the second period, and location coordinates of the first probe having changed by at least a predetermined location change threshold in the second period, identify a third period after the second period, wherein third readings received by the processor from the force sensor are indicative of a second change in the measured contact forces between the probe and the cavity by less than the predetermined limit over at least the predetermined interval of time, and second signals received by the processor are indicative of a second change in the measured value of the proximity by less than the predetermined proximity change threshold and calibrate a zero-force point for the force sensor according to the third readings. a first probe configured to be inserted into a cavity in a body of a subject; a force sensor located within the first probe; a second probe configured to be inserted into the cavity in proximity to the first probe; and a processor, configured to: identify a first period wherein first readings received by the processor from the force sensor are indicative of a first change in measured contact forces between the first probe and the cavity by less than a predetermined limit over at least a predetermined interval of time, and first signals received by the processor are indicative of a first change in a measured value of the proximity by less than a predetermined proximity change threshold; identify a second period after the first period, wherein second readings received by the processor from the force sensor indicate that one condition is met from a set of conditions consisting of: the second readings having changed by more than a predetermined force threshold in the second period, and location coordinates of the first probe having changed by at least a predetermined location change threshold in the second period, identify a third period after the second period, wherein third readings received by the processor from the force sensor are indicative of a second change in the measured contact forces between the probe and the cavity by less than the predetermined limit over at least the predetermined interval of time, and second signals received by the processor are indicative of a second change in the measured value of the proximity by less than the predetermined proximity change threshold and calibrate a zero-force point for the force sensor according to the third readings. identify a first period wherein first readings received by the processor from the force sensor are indicative of a first change in measured contact forces between the first probe and the cavity by less than a predetermined limit over at least a predetermined interval of time, and first signals received by the processor are indicative of a first change in a measured value of the proximity by less than a predetermined proximity change threshold; identify a second period after the first period, wherein second readings received by the processor from the force sensor indicate that one condition is met from a set of conditions consisting of: the second readings having changed by more than a predetermined force threshold in the second period, and location coordinates of the first probe having changed by at least a predetermined location change threshold in the second period, the second readings having changed by more than a predetermined force threshold in the second period, and location coordinates of the first probe having changed by at least a predetermined location change threshold in the second period, identify a third period after the second period, wherein third readings received by the processor from the force sensor are indicative of a second change in the measured contact forces between the probe and the cavity by less than the predetermined limit over at least the predetermined interval of time, and second signals received by the processor are indicative of a second change in the measured value of the proximity by less than the predetermined proximity change threshold and calibrate a zero-force point for the force sensor according to the third readings.