Abstract: An opto-electronic scale-reading apparatus comprising a read head and a scale supported for displacement relative to each other for the incremental reading of marks provided on the scale. The read head includes a light source for producing light rays incident on the scale, an index grating for diffracting readable rays into fringes in at least one order of diffracton, and an analyzer grating for converting the fringes into light modulations at a rate which is a function of the rate of displacement between the read head and the scale. The scale comprises an elongate member having marks spaced in the direction of its length and spaces defined between the marks. The marks and spaces are defined by respective first and second surfaces of surface portions of the members, the first surfaces laying at an angle to adjacent second surfaces so that incident rays are reflected by the first surfaces in a first direction to be readable by the read head in the first direction.

Abstract: A metrological scale for use in optoelectronic scale reading apparatus comprising a tape made of spring steel and having a surface layer of copper. The scale has scale marks constituted by a zig-zag or other profile impressed into the surface layer by a rolling process. During rolling, the relatively soft copper is readily deformed to accept the profile while the spring steel resists plastic elongation of the tape.