That's the simple explanation I can find every now and then. I want a bit more detail - how is the phase shift determined, for starters, and how can it be integrated with such high precision to give the rotation? There has to be a few tricks to it.. .. .That only works for one kind of RLG too, forgot the specific term but it's the one with the laser outside of the resonant cavity. The other kind where the laser crystal is actually within the cavity supposedly creates a standing wave in there which is star fixed. Understanding a laser gets me a long way towards being able to figure that one out, but I'd still like the details. If for nothing else, the to confirm my homebrewed understanding.. .. .Once you have the standing wave, one photodetector can count the number of nodes as the RLG is rotated about its sensitive axis and with another one an odd number of quarter wawelenghts away, you can determine the direction of rotation. But... (now it's starting to sound familiar, innit <img border="0" title="" alt="[Smile]" src="smile.gif" /> ) ...DETAILS?!. .. .Then there's phase locking, exactly how the oscillator prevents phase locking... etc etc etc.. .. .Cheers,. . /ft