Zero positioning, new ideas

Lately I have been working on mounting an Open Source 3D printer called RepRap(Version 1.0, Darwin). While working on it, I learnt about their brilliant idea for Zero Positioning. They use a tiny beam light sensor(Opto endstop V2.1) which is interrupted by a small stick which is connected to the moving joint. The interrupted state defines that the moving joint is in the zero position.

Picture from : RepRap Blog