A number of early elevating innovations were to regain their popularity in modern times; the traction drive was first developed as an adjunct to a steam-driven mine hoist. The modern traction machine was more compact than the drum machine, just as the latter had taken up much less space than the roped hydraulic drive. As buildings became taller, the amount of hoist cable wound around the drum became lengthier and the drum wider, with the lead of the single or dual hoist ropes shifting from one side to the other. On the other hand, the traction drum was narrow, and the lead from the greater number of hoist ropes always remained straight and centered. A problem with the traction drive was rope slippage in the drum grooves. Calculations were developed for carefully formed grooves and for the proper sized rope of the correct metal composition and construction. Rope became an even more important accessory. Slippage had a benefit; if a car or counterweight overran a terminal, the slippage in the traction sheave would eliminate the kind of damage that would occur with a drum type should the car or counterweight strike the overhead and the ropes be pulled out of their sockets. Without the manual terminal stops built into the water hydraulic and electric drum machines, a greater reliance was placed upon electrically operated directional and final limit switches placed appropriately in the hoistway.