The C3D specification expects physical measurements to be one of two types, either positional information (3D coordinates) or numeric data (digital analog information).

Each 3D coordinate is stored as a raw X, Y, and Z data samples with information about the sample – accuracy (the average error or residual), and camera contribution (the specific observers or cameras used to produce the data).

Each sample of numeric data can contain digitized analog information from sources such as EMG, Goniometers, Load Cells, and Force Plates etc.  These samples are synchronized to the 3D coordinate samples so that it is easy to determine the correct numeric data values that relate to any 3D sample within the file.  If desired (for high analog sample rates etc.), the C3D format can store multiple numeric analog samples per 3D coordinate sample. 

As a result, many C3D files contain both analog and 3D data synchronized frame by frame.  This is a big improvement over the common situation of multiple OEM formats that usually stored parameter data, analog data, and 3D data, separately in multiple files.  Storing all the related information in a single file gives a greater degree of confidence in the data.  It is easier to retrieve the relevant data and increases the confidence that data from multiple sources such as cameras, video equipment and force plates is synchronized in time and 3D space.