[Kevin Sevcik]

The index is a line that pulses exactly once per revolution.

I can't think of any FRC applications that would require it. In industry, you use the index pulse in combination with a home switch to determine an absolute zero location for a motor. Physical switches are notoriously inconsistent, so to zero a location consistently, you set zero at the point when the home switch is on and the index pulse happens. As long as the index pulse happen a reasonable distance from the switch turning on, you have a very consistent zero point.