Measuring: The quantifying art

The photograph of a comet or asteroid against background stars contains information in analog form regarding the relative positions of comet and star images. Measuring is the procedure for covnerting this information to digital form for computation of the object's accurate equatorial coordinates at the time of observation. The use of one- and two-coordinate measuring engines to measure the positions of images which may be elongated, comatic, or both, as well as round images is discussed along with the training of novice measurers to cope with such images. The grading of plates for potential accuracy of positions, preparation of plates for measuring, the accuracy of measurement, effects of telescope focal length and reduction technique upon the accuracy of positions, and the procedures and checks which may prevent erroneous positions also are discussed.