... The first part of the algorithm (which is described in the sensitivity task documentation) calculates the minimum counts within the detection box which would just be detectable; in order to convert this counts-within-a-box to total count rate of the whole source , esensitivity needs to know the ratio between the two across the width of the instrument field of view. ... econvolverprep first creates a list of small convolver images, each of which is the PSF truncated within the detection box. ...