An approach to summarizing interrelations between functions used in radiotherapy dose calculations is suggested. A mnemonic diagram is proposed which should be useful for radiation physicists in radiotherapy to obtain at a quick glance the definitions and interrelations between the commonly used functions like back‐scatter factor, percent depth dose, tissue–air ratio, scatter–air ratio, and scatter function. The conditions under which the measurements must be made for these functions and interrelations to be valid are described. Rules for application of the diagram and some practical examples are included. The diagram also serves as a very effective teaching aid.