Small and large telescopes are being installed all around the world. Astronomers have thus acquired better access to more modern equipment; not in the least to photometers, which are very important tools for the contemporary observer. This development of higher quality and more sensitive equipment makes it very necessary to improve the accuracy of the measurements. This guide helps the astronomer and astronomy student to improve the quality of their photometric measurements and to extract a maximum of information from their observations. The book is based on the authors' observing experience, spending numerious nights behind various instruments at many different observatories.