The sensing system for coordinate measurement equipment has a sensing head (1) which produces sensing signals and which has a holder (8) for sening pins which can be replaceably mounted on it. A further sensing head (23) smaller than the first can be attached to the first head's sensing pin holder. An arrangement which switches over between the signals of the first and second heads is connected to a mechanism for varying the bias force in the first head. Both sensing heads are of the switching type. Each has a contact sensitive sensor (10,20) and a switch which responds to deflection of the sensing pin.
