Revised with substantial editorial changes throughout to improve readability, i.e. the replacement of the word “REAL” with the more common term “floating-point.” The description of the structure of parameter files has changed substantially and several pages have been added to describe the calculation of analog scale factors, particularly with reference to force platforms. The manual now includes examples of the calculations for each type of force plate. A short description of the history of the C3D format has been added to the introduction.