Abstract: An improved tape measure having a casing with a retractable measure tape coiled therein, and carpenter's square blade structure secured to the casing. The carpenter's square blade structure is pivotally attached to the casing thus allowing it to be moved into and out of engagement with the side walls of the casing whereby a line may easily be scribed perpendicular to the longitudinal axis of the measuring tape by running a marking instrument along the forward edge of the carpenter's square blade structure on the surface to be scribed. The casing has recesses formed in the side walls for receiving the arms of the carpenter's square blade structure. Within these recesses, magnets have been inserted to hold the arms of the carpenter's square blade structure in a folded up position. The carpenter's square blade structure may be detachably mounted on the bottom wall of the casing.