The methods used for the S and C mode are correct for unweighted events and
Poisson statistics for one or two-dimensional histograms.
For weighted events,
a Gaussian approximation is used, which results in DIFFS values which are
too low when there are fewer than 25 or so ``equivalent events'' (defined
under HSTATI) per bin.
This is caused by either few entries or by wide fluctuation in weights.
The result is that HDIFFB rejects to many bins in this case.
Comparisons for profile histograms assume Gaussian statistics
for the S and C mode comparisons of the channel mean.
Fewer that 25 or so events will result in DIFFS values which are too large.
The result is that HDIFFB rejects too many event in these low statistic cases.