Small and large telescopes are being installed around the world. Astronomers have thus acquired better access to more modern equipment; not in the least to photometers, which are important tools for the contemporary obsserver. This development of higher quality and more sensitive equipment makes it necessary to improve the accuracy of the measurements. This guide aims to help 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 time behind various instruments at different observatories.