PS: This algorithm is not actually dealing with any absolute angles relative to the ground below.
If it senses a (+) gyro signal in a particular axis, it will drive the appropriate motors untill it receives a gyro signal that reverses in the opposite direction through gyro centre, continuing untill a (-) signal of same proportion as original (+) signal is received. Then waits for this (-) signal to come back to centre again. It then considers that it must have corrected for the error and brought DF back to our sample reference position. It is in fact performing this task with it's eyes closed, in reality. It relies on the pilot to make any small adjustments if it doesn't perform this task perfectly.

Cheers ADI