... Ballet, J. 2001, in ASP Conf. ... The underlying hypothesis is that an event is due to only one X-ray. ... The charge from an X-ray may either concentrate in one pixel (single events) or appear over several adjacent pixels (split events) forming a specific pattern or grade. ... I have shown (Ballet 1999, Equations 1-3 and A5) that for strict (0) and generalised (30) single events (using the above notations), assuming a (locally) uniform X-ray flux, i.e., a pixel size small with respect to the PSF: ....