is expected to vary [*during*]{} a burst. All of these factors are reflected in the observed values and evolution of [$E_{\rm peak}$]{}. However, it is clearly true that [$E_{\rm peak}$]{} arises from some [*physical*]{} emission process, so on top of the known sources of potential variation on the observed quantity, there is an unknown intrinsic distribution in [$E_{\rm peak}$]{} that is related to the underlying physical processes. This intrinsic distribution may be quite wide, as can be seen in the time-resolved spectra of single-pulse bursts where the redshift is known, like GRB110721A [@axelsson] and the first pulse of GRB130427A [@preece2014]. In each of these, hard-to-soft spectral evolution was observed, with [$E_{\rm peak}$]{} varying over considerably greater than one decade in energy. Despite the supposition that each of the contributions to the variation in [$E_{\rm peak}$]{} should operate completely independently, the overall distribution of fitted values of [$E_{\rm peak}$]{} is less than a decade in width (e.g.: Figure \[BATSE\_GBM\_Epeak\], discussed below), whether the distribution is drawn from the average spectra of a large sample of bursts [@GoldsteinCat; @NavaCat; @GruberCat] or from statistically independent time-resolved spectra from bright bursts [@KanekoCat]. Much has been made of broad correlations between [$E_{\rm peak}$]{} and other 