difference which of the two (or three) is connecting. When access to more outlets was required, the rotor had two sets of wipers opposite each other but offset vertically: on the first half rotation one set of outlets was accessed; the second set of outlets was accessed on the second half rotation. An electromagnet advances (steps) the wipers to the next position when fed with a pulse of DC. The magnet's armature (spring-loaded) operates a pawl that advances a ratchet. When the pawl reaches its full stroke, it blocks the ratchet so it and the wipers will not overshoot. When power to the coil disconnects, the spring retracts the pawl. Another pawl, sometimes called a detent spring, pivoted on the frame ensures that the wipers do not move backward; contact friction keeps them in place. Some uniselector designs step on application of the operate pulse; others step on its removal. In most applications, such as telephony, it is desirable to be able to return the wipers to a "home" position; this is at the beginning of rotation, at one end of the array of fixed contacts. Some switches have a cam attached to the wiper shaft. This cam operates a set of contacts when the wiper is at home position, which is at the beginning of the span of rotation. Other circuit designs used one level (pole) of the contacts to home the wipers, so the separate homing contacts were not needed. Typical stepping switches have contacts directly operated by the stepping magnet's armature; these contacts can serve to make the magnet cycle ("self-step") and advance the wipers as long as power is applied. The external control circuits remove power when the wipers reach the desired position; that could be the home position. Most stepping switches rotate the wipers in only one direction, but some are bidirectional; the latter have a second magnet to rotate the wipers the other way. A third variety "winds" a spring as the wiper steps progressively, and a ratchet holds the wipers from returning to home position. When the circuit is no longer needed, another electromagnet releases the holding pawl; the spring then returns the wipers to their home position. Stepping switches were quite noisy in operation (especially when self-stepping), because their mechanisms accelerated and stopped quickly to minimize operating time. One could compare their sound to that of some snap-action mechanisms. Nevertheless, they were