  The comparison of visual magnitudes of stars compiled in old catalogues is
expected to yield information about their long-term magnitude variations. In
seven old catalogues whose historical data have been intensively compared, 2123
sampled stars have been studied, disregarding stars that we could not identify,
double stars which could be misidentified, or stars observed under poor
conditions, and known variable stars with large amplitude discrepancies. The
independence of stellar magnitude catalogues is demonstrated by comparing seven
old studies to each other, suggesting that the magnitude estimates in each
catalogue reflect the brightness at each observational period. Furthermore, by
comparing them with a modern star catalogue, the magnitude differences show a
Gaussian distribution. Therefore, if they are sufficiently larger than the
deduced standard deviations, the magnitude variations between the catalogues
can be considered real. Thus, the stellar magnitudes compiled in old studies
can be used as scientific data within the average intrinsic uncertainty. These
seven old catalogues can be used as data for the survey of the long-term
variability of stars.
