1,203,368. Detecting location of movable object. BENDIX CORP. 22 Nov., 1968 [18 Dec., 1967], No. 55512/68. Heading G4H. In apparatus for detecting the location of a movable object relative to a predetermined limit 10 (Fig. 2) determined by two independent photo-electric sensing members 26, 28 spaced by an amount less than the dimension of the object, the output signal from circuitry 34 connected to the sensing members determines the position of the object relative to the limit 10. In the embodiment described for determining the position of a float 6 relative to two limits 10, 10<SP>1</SP>, photo transistors 26, 28; 26<SP>1</SP>, 281 deliver a high output signal when the float intercepts the light impinging on them, this signal being fed via inverting transistors 30, 32; 301, 32<SP>1</SP> to bi-stables 34, 34<SP>1</SP> comprising NAND gates 48, 40; 48<SP>1</SP>, 401 controlling lights 12, 14, 16 to indicate the position of the float. The operation of the circuitry is such that with the float below 10<SP>1</SP>, the outputs of gates 38, 38<SP>1</SP> are low and consequently light 16 is switched on via NAND gate 52. The outputs remain low as the float moves pass sensor 281 until it also passes sensor 26<SP>1</SP> when the output of gate 38<SP>1</SP> switches to illuminate light 14. Changes in the outputs of the gates 38, 38<SP>1</SP> occur when the float passes sensor 28, gates 38 changing state to illuminate light 12 when the float covers either both sensors 26, 28 or only sensor 26. The apparatus may alternatively be used for sorting by replacing the lights by relays actuating segregating gates.