To characterize the polarimeter it is necessary to know the , however, finding the greatest does not optimize the performance of the polarimeter. Instead it is necessary to maximize a quantity called figure-of-merit (FOM) which, for polarimeters, is often defined as
where N is the total number of events counted in the detector. When FOM is maximized the uncertainty in the measured neutron polarization is minimized. This is done by applying a number of cuts to the final reduced data set (described in section ) to get the best results, as defined by FOM. The cuts which are applied to the data are described below.