what is described is a length measurement system and method for measuring relative movements between first and second machine parts , said measurement system comprising a sensing head and a rule sensed by it , said sensing head being securely mountable on the first machine part and said rule being connectable with the second machine part during final assembly of the length measurement system , wherein the rule is mounted within a profiled part which is securely mountable on the second machine part in final assembly and into which the sensing head protrudes , said sensing head being preadjusted , via a removable mounting element , and being releasably connected with said profiled part , in a state prepared for final assembly , or said sensing head , when finally assembled , protruding into the profiled part without being supported thereon .