1,246,756. Measuring lengths. TOKYO SHIBAURA ELECTRIC CO. Ltd. 15 April, 1970 [16 April, 1969], No. 17891/70. Heading G4H. Apparatus for measuring the width of a steel sheet 10, comprises an extended light source 11 and a photo-electric detector unit 13. The unit 13 is scanned from stop switch 27 across the steel plate to stop switch 28. The photoelectric detector detects when the steel plate is beneath the detector and sends a signal to enable gate 30. Unit 13 also carries a magnetic pick-up 21 which operates in conjunction with a magnetic scale 22 having magnetic pulses recorded thereon to produce a sequence of equiweighted pulses. These pulses pass through gate 30 to a counter 29, since gate 30 is only open while the detector is over the steel sheet 10 the count gives a measure of the width of the sheet. Switch 26 activates the unit, and switches 27 and 28 cause a reversal of the direction of the scan, so that successive scans on different sheets are performed in opposite directions. Modifications are described in which the device used for detecting the sheet operates with a laser beam, by reflected light from the steel sheet, by radiation from the sheet itself, using a fluidic proximity detector, and using magnetic or capacitative proximity heads.