A capacitive sensor to determine instantaneous angular position of a rotatable element in a timepiece, such as a setting stem of a wristwatch. Static electrodes are configured to form, in conjunction with rotor electrodes of the rotatable element, a first differential capacitance pair and a second differential capacitance pair. A sensor calculation unit is configured to sense difference values from the differential capacitances pairs and to evaluate the angular position of the rotatable element from the difference values using predetermined information relating the differential capacitance values to angular position values.