Master controllers, located in the crane operator's cabin, shall be used to effect the Main Hoist, Trolley and Gantry operation. The controllers shall be digital type, standardised and interchangeable among the cranes supplied under this contract. They shall be spring returned, positively indented at zero notch and released by push-down interlock catch incorporated into the master controller. Off position interlocks shall be provided for the master controllers so that they have to be returned to the off position for re-staring of crane drives after unintentional stopping. Simultaneous operation of Main Hoist motion and Trolley Travel motion (both motions at variable speeds) shall be available.