Information on the C code procedure SPD_GetAvrgMecSpeedUnit ?

In the FOC motor code the average mechanical motor speed is returned by procedure SPD_GetAvrgMecSpeedUnit which simply returns a value pointed at. I'd like to know the details of how the average is done and over what period of time and what sample rate. I believe it may be using a define STO_FIFO_DEPTH_UNIT from drive_parameters.h but am not sure of this.

Any documentation or discussion of this would be helpful to my project.

Thanks,

Brian