The ANALOG:FORMAT parameter is a character data array that consists of a single ASCII (A-Z, 0-9) string that documents the analog data format used within the C3D file.  The parameter has two possible values: SIGNED or UNSIGNED.  This specifies whether the 'data' format (rather than the 'storage' format) is 2's compliment or offset binary respectively.  This parameter applies to all analog data values within the 3D and Analog data section.  It should normally be “locked”.

If the ANALOG:FORMAT parameter contains the string “SIGNED” then the C3D 'storage' format for both the data samples and the ANALOG:OFFSET parameters must also be “SIGNED”.  This is the default storage method for all analog data values, irrespective of resolution and allows data to be stored using signed integer values from -32768 to +32767 representing both positive and negative input signal excursions.

If the ANALOG:FORMAT parameter contains the string “UNSIGNED” then the ANALOG:OFFSET parameters must also be treated as “UNSIGNED” values.

If the ANALOG:FORMAT parameter does not exist the it should be assumed that its value is SIGNED unless the analog data contains 16-bit values, in which case UNSIGNED is a possibility.