I should have commented on this chat before now, but here goes anyway. The BAA VSS also has a large database of observations of nearly 2 million observations (albeit not as large as the AAVSO's) with observations of a few stars stretching back over 100 years. We also exchange data with the AAVSO and the RASNZ (the latter mostly of southern stars). ALL VSS observations for many years have included the full estimate in the reporting log. This means that if a comparison star's magnitude is found to be grossly in error (or even variable!) it is possible to recalculate the deduced magnitude using the correct value. This also allows observations to be checked for any arithmetical errors etc. Also, as Taichi Kato pointed out, most VS organisations (all?) are using the standard Johnson V system for their comparison star sequences nowadays, and this, of course, includes the BAA VSS. Regards, Roger Pickard, Director, BAA Variable Star Section, England. Tel: 01732 850663 (Int: +441732850663) E-mail: rdp@star.ukc.ac.uk BAA VSS Web Page: www.telf-ast.demon.co.uk/