Abstract: A coilable tape rule includes a pair of rollers that are convexly rounded in both axial and transaxial planes, about which rollers the measuring blade moves during passage through the casing and which cause the blade to turn on its longitudinal axis so as to reorient its width dimension to a perpendicular relationship to the axis of coiling. The blade is of concavo-convex cross section and cooperates with the rollers for tracking control and to enhance the smoothness and reliability of extension and retraction.

Abstract: A coilable tape rule includes a fixed structure or a roller about which the measuring blade moves during extension from the casing and which causes the blade to turn on its longitudinal axis so as to reorient its width dimension to a perpendicular relationship to the axis of coiling.

Abstract: A computer controlled impact printer has a replaceable ribbon guide assembly mounted on a printhead. The assembly is movable vertically between at least two stable positions. Each position places a differently colored portion of the ribbon between the printhead and a sheet of paper. Rotation of a pair of opposed cams changes the vertical position of the assembly. One cam is fixed and the other is rotatable by a pawl operating on a ratchet wheel secured to the cam. The pawl is mounted on the assembly for a longitudinal sliding movement. Movement of the printhead to a preselected position at or near one end of its travel path drives the pawl into an abutment surface which displaces the pawl a predetermined distance. The displacement rotates the movable cam from one stable vertical position to another. The mating cam surfaces preferably have matching sawtooth configurations with recesses formed in the tips of the teeth of one cam.