Abstract: A controlling device adapted particularly for use with rental equipment wherein it is desired to control or limit the time of operation of the rented equipment. The unit comprises a spring-wound motor which will wind down upon expiration of the rental time and cause a switch to open to thus cause a cessation of operation of the rented equipment. A key is employed for effecting the rotation of one of a plurality of arms which will in turn actuate an arm extending from a counting mechanism which will indicate the amount of time the rented equipment has been previously paid for by the rentor of the equipment.