Automatic calibration of oscillator scales

THE USE of heterodyne oscillators in testing and maintenance of carrier telephone systems has created the problem of designing long frequency scales of high accuracy and good readability. It has been found that for panel-mounted equipment with a well illuminated scale to be read at arms length the scale modulus should be such that the smallest interval which it is desirable to read is not less than 0.05 inch. For carrier system applications, the corresponding frequency interval is independent of the frequency and so the correct choice is a linear scale.