A sterile, hand-held manual surgical instrument intended to be used during mitral valve repair to determine the proper length of a chordal replacement prosthesis used to repair the chordae tendinae. It is a slender tool with a gauge and extendable distal hooks designed to measure the distance between the edge of the valve leaflet and the planned site of attachment of the chordal replacement to the papillary muscle. This is a single-use device.