In the Cornish examples the motive power was provided by waterwheels, or one of the mine's steam engines. The steam engine or water wheel would be linked to a series of beams – known as "rods" – fastened together and reaching to the bottom of the mineshaft. These were arranged to offer a reciprocating motion of, typically, twelve to fifteen feet (three to five metres). Small foot platforms were attached to the rods at the same distance apart as the engine stroke and fixed platforms ("sollars") were built onto the shaft walls, spaced to coincide with the top and bottom positions of each of the moving platforms. The moving platforms were often small, typically square, to make the miner stand close to the centre-line of the rod and thus keep a safe distance from the sides of the shaft. For the same reason the grab handles were always fitted directly above the foot platforms. To go up or down, the miner would step onto the travelling platform and allow himself to be carried to the next fixed platform, where he would step off and wait. At the end of the next stroke the next moving platform would line up and he could step onto it and repeat the process. Miners could ascend and descend at the same time: the pause at the changeover point was made long enough (typically between two and eight seconds) for two men to change places. To facilitate this some installations (such as at the Devon Great Consols mine, Tavistock) had a fixed platform at both sides of the shaft, one side for miners descending and one for those on the ascent. Counterweights – large boxes filled with stones attached through "see-sawing" horizontal beams – were installed to avoid the full weight of the shaft and men bearing on the top linkage. In the deepest mines, which could sink to more than 350 fathoms (640 metres), extra counterweights were provided at regular intervals, in horizontal side galleries.