In a retention device, a medical robot and a method to set the tool center point of a medical robot, the retention device has a fixing device to fix the head of a person held by the retention device. The fixing device provides an indication of the position of the openings of the auditory canals of the ears of the person relative to the retention device based on the relation between the fixing device and the head of the person and the relation between the fixing device and the retention device.
