The locomotive's forward and reverse control, which is also used to adjust cut off to vary the steam admission and expansion cycles in the cylinders. The direction of movement for a locomotive is decided when starting by determining which direction each piston must move first. This is done by adjusting the position of the valve gear of each cylinder with a reverser so that the first admission of steam will force the piston in the right direction to achieve the desired direction of wheel rotation. A lever or handwheel is provided in the cab to control the reverser. It has three principle positions, Full Forward Gear, Mid Gear and Full Reverse Gear. Mid Gear is equivalent to 'neutral' on a road vehicle. There are also intermediate positions to adjust the 'cut off' point for steam admission to the cylinders. An indicator is provided to show the driver the 'cut off' position and the reverser lever is fitted with a locking ratchet to hold it in the required position. Reverser levers are usually purely mechanical devices and require some effort to operate effectively while the locomotive is running since the valve gear is under considerable pressure from steam. Some locomotives are fitted with steam operated reversers.