US Patent 7164120 Position measuring instrument

A method for position measurement that includes scanning a plurality of graduation periods of one incremental graduation by a detector arrangement extending over a length of one measurement range, a reference marking being integrated with one of the graduation periods, and generating a plurality of periodic scanning signals, of which at least one is locally modified by the reference marking. The method includes detecting the at least one scanning signal, modified by the reference marking, from among the plurality of periodic scanning signals. The method further includes determining an absolute position of the reference marking within the length of said measurement range as a function of the scanning signal detected.