Precision Differential CCD Photometry

In this paper we describe the technique and reduction procedure in use at the SAAO for differential CCD photometry. Much of this work involves the detection of microvariables in galactic and Magellanic Cloud open clusters. The large number of frames requires automated cleaning and reduction software (principally the DoPhot package) which is briefly described. The process of selecting comparison stars and the technique of detecting low-amplitude variables is discussed. The software is well suited to be used for on-line reductions at the telescope and a start has been made in this direction. Finally, some astrophysical results involving precision differential CCD photometry are described.