The method presented in the preceding section for subtracting accidentals from tagged spectra is equivalent to keeping a single copy of every analysis histogram and using a weight factor to keep track of the tagging information. The weight factor is calculated as follows. For every hit in any tagging counter that falls inside the coincidences window the weight factor is incremented by one, and for every tagger hit inside the accidentals window the weight factor is decremented by one. This leads to some events having a weight factor of zero, i.e. being ignored, but that is inevitable in an analysis where spectra are being subtracted. Viewed in this way, the method admits a straight-forward error analysis. Histogramming packages such as HBOOK have built-in facilities to track the statistical errors associated with weighted events.