Position-sensing unit and multidimensional pointer comprising one or more such units

A position-sensing unit for determining a relative position in at least one dimension, said position-sensing unit comprising:

• a detector with at least two fields each having a radiation-detecting surface, wherein each of the at least two fields includes a radiation-spreading medium, which constitutes the radiation-detecting surface and which coacts with a separate detection unit associated with the field,
• a radiation source for emitting radiation to the respective fields, radiation detected by one field being distinguishable from radiation detected by other fields,
• a screen element which is arranged in the beam path between the detector and the radiation source and which, for each determination of a position and seen from the perspective of the radiation source, partially screens off at least one of the fields but does not completely screen off any one of the fields,
• at least one of the detector and the radiation source being so movable relative to the screen element in a first direction transversely of the direction of the radiation that such a relative movement causes a relative change of the screening-off of the fields, and
• means for determining a relative position in said first direction between the screen element and at least the one of the radiation source and the detector, based on a comparison between radiation which is detected by the detector and which falls on the respective radiation-detecting fields.