evselect also contains the facility to produce a general FITS histogram product, which does not have the constraints imposed on it by the OGIP compliance of light curves and spectra. This is enabled by seting the histogram output file, which is specified with the parameter histogramset. The column from which to extract the histogram is set with the parameter histogramcolumn.
The range of the histogram is set using the same algorithm as for setting the energy range in a spectrum, using the parameters histogrammin and histogrammax. The bin size is set with the parameter histogrambinsize. Real valued columns are supported. All range and binning parameters are in the units of the column from which the data is being extracted.
When a histogram table is created, it contains two columns, one named after the column from which it was extracted, and another named COUNTS. As with light curves, one can accumulate the values of a column from the input table, instead of just counts, by setting the parameter zcolumn. In this case, an ERROR column is also created in the output table, and its value is based on the parameter zerrorcolumn, as with light curves.
