Capacitance diaphragm gages which were previously known as capacitance manometers, have become a ubiquitous part of systems used in the vacuum community because of their ease of use, compatibility with most gases, and potential accuracy and resolution. They are used not only as pressure measuring devices, but also as transfer standards against which other pressure instruments are calibrated. There are a variety of precautions that must be considered when using these instruments. The American Vacuum Society is therefore presenting this Recommended Practice as a guide to their proper calibration and use as transfer standards. The document covers suggested plumbing configurations, laboratory practices, calibration methods, and reports.