  A significant amount of data on the historical and current behaviour of
variable stars is derived from visual estimates of brightness using a set of
comparison stars. To make optimum use of this invaluable collection one must
understand the characteristics of visual photometry, which are significantly
different from those of electronic or photographic data. Here I show that the
dispersion of estimates among observers is very consistent at between 0.2 and
0.3 magnitudes and, surprisingly, has no apparent dependence on the colour of
comparison stars or on their spacing in brightness.
