Published online by Cambridge University Press: 12 April 2016
A little more than a century and a half has passed since F.G.W. Struve began to provide the astronomical world with visual double star measures of both quantity and quality. Since that time, nearly a million individual measures have been made by all techniques, and most of these are now available in machine-readable form in the punch-card Observation Catalog maintained at the Naval Observatory. As of 1 March 1981, this Catalog contained 877242 measures grouped into 398818 means. The data file is now virtually complete for all 20th century observations, and perhaps 80% complete for the 19th century material. Additions are being made steadily and we can look forward to having a complete set of observations for every known double star in a few more years.