The position of a photon in the detector is calculated from the
signals measured on the two wedges (
and 
) of the
wedge-and-wedge cathode. The position is given by the formula:
0.1 in
0.1 in
In the BCS this calculation is done using a look-up table held in ROM.
Because of the quantized nature of this digital technique, solutions
sometimes fall either side of the value that would have been
determined with an analogue technique and spikes and dips are seen in
what should be a flat field. The position of these can be calculated,
and corrected - there is some dependence on the energy of the detected
photon. No photons are lost, they are merely displaced into adjacent
bins so integrations under curves are not affected, but when fitting
spectra it is best to avoid those bins.