Abstract: A measuring instrument (2) for use during an orthopaedic surgical procedure to measure first and second distances from a reference point on a bone to first and second measurement points respectively. The measuring instrument has a first scale (24) for displaying the first distance and a second scale (28) for displaying the second distance. It includes a mask (26) which can be positioned against the second scale after the first distance has been measured in a position that is selected relative to the second scale dependent on the measured first distance, to restrict the length of the second scale that is visible to the user.