1,203,636. Rack and pigion gearing. DYSONA INDUSTRIES Ltd. 28 May, 1968 [30 May, 1967; 24 July, 1967], Nos. 24877/67 and 33879/67. Heading F2Q. [Also in Division H1] A timing unit for a microwave oven associated with a food-vending machine is controlled by an elongated key 10 of plastics material which is inserted into a slot 24. A rack 16a, 16b extending the length of the key 10 is then engaged by a toothed wheel 12 continuously driven by a motor 26 at 4 r.p.m., for example, and the key is thus drawn through the unit and fed into a key basket, not shown. The passage of the key 10 rotates a narrow toothed wheel 14 by an amount depending upon the length of a shorter rack portion 18. Wheel 14 is connected to a motor 28 by a slipping clutch (20, Fig. 1, not shown). When the oven is switched on the motor 28 drives the wheel 14 back to its starting position where a pin 22 re-engages a lever 30 to open switch 32 and de-energize the oven. Several keys may be inserted consecutively to provide a cooking time corresponding to the total length of their rack portions 18, and a solenoid-operated shutter (not described) may close the slot 24 to prevent the wheel 14 being thus set more than a complete revolution. Keys having other rack arrangements are disclosed in Figs. 5a, 5b and 5c (not shown), those of Figs. 5b and 5c requiring modification of wheels 12 and 14.