The FORCE_PLATFORM:ZERO parameter is an array that contains two non-zero signed integer values.  These specify the range of 3D frames that may be used to provide a baseline for the force platform measurements.  Most software applications seem to set the range to 1,10 although other ranges are acceptable.  Some applications may specify a range of 0,10, which should be interpreted as a range of 1 to 10 since the C3D file does not have a 3D frame number 0.

This allows any application that reads the force plate data to read in the analog data for the given frames, find the mean for each channel, and subtract it from the analog data for the corresponding channel as it is accessed for force platform displays.  If the two frame numbers provided are both zero then no baseline-offset correction should be applied - any other value defines a range of 3D frames.

Note that the presence of this parameter does not mean that any baseline correction will be performed – only that if it is performed it should use these values.  If you do implement baseline correction in an application then you must be careful to ensure that the baseline correction is only applied to the specified force plate channels and that the force plates are unloaded during the frame rage specified by the parameter.