This function may be performed alone by calling the script with entrystage and finalstage=`bias'.
Note that action is taken only if the merged source list contains a keyword COMPARED which has the value `T'. This keyword is written to the lists of detected sources by the task srccompare, called as part of default eimsim functioning.
The function calls a task eimsimbias, which constructs some histograms from the merged list of detections, with the aim of comparing the detection procedure's estimates of the values of position and flux with the true values. The estimated uncertainties in these parameters are also compared with the scatter in the estimates around the true values. As you can see from the description in the eimsim documentation of the procedure which attempts to match detected with simulated sources, it is vital that the detection procedure calculates accurate estimates of not just the position and flux of each source, but also the uncertainties in these quantities. The histograms created in the present section can help one to determine if there is a bias in any of these quantities.
Six histograms are made and all are written to separate tables in the output dataset. These histograms are described in the following subsubsections:
each of the input source-list columns X, Y and FLUX: makes a frequency histogram of relative 
offset.
XMM-Newton SOC/SSC -- 2016-02-01