The index for the Measurement Interval within this PM session. Measurement Interval indexes are assigned sequentially by the device. The first Measurement Interval that occurs after the session is started is assigned index 1. Referential integrity is necessary, i.e., the index needs to be persistent upon a reboot or restart of a device. The index is never reused while this session is active until it wraps to zero. The index value keeps increasing up to that time.