> Sorry Steve > You forgot the luminiferous aether ... > http://en.wikipedia.org/wiki/Luminiferous_aether Link from that to article relevant to optical gyros http://en.wikipedia.org/wiki/Sagnac_effect -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist