| However, in August 1994 the Museum learned that the American instrument dealers ‘Tesseract’ were in possession of a medieval lunar volvelle plate which had been in a private collection for many years and before that with a London dealer. This plate had a scale of 291/2 divisions, the conventional representation of the lunar cycle, with a pointer at its origin. When in use, it would have rotated at the centre of a zodiacal scale and, with the pointer set to the position of the sun, an index arm moving above the plate would have been rotated to the age of the moon in order to indicate the zodiacal position of the moon on the outer scale.|
Since this volvelle was an example of the principal missing component from the Museum’s quadrant, and since a similarity in the engraving style had already been noted, the Museum became interested in acquiring the plate to accompany and display alongside its instrument. As Tony Simcock, who was taking care of the Museum’s side of the correspondence, gathered more details about the volvelle plate, excitement grew at the increasing convergence of the two sets of photographs and measurements. Even if it was difficult to admit the thought that they really belonged together, it became imperative to purchase the plate for the Museum and this was done with the help of a grant from the PRISM fund of the Museums and Galleries Commission.