In this design, there are 24 line finders. If any of the 100 subscribers has to get access to any of 24 two-motion selectors, it is necessary that every line finder is capable of reaching any of the 100 subscribers. In other words, every line finder should have 100 outlets. For this purpose, two motion selectors have to be used as line finders. Configuration is displayed in figure. Corresponding outlets of the line finders are commoned. In the same way, outlets of the numerical selectors are also commoned.

When start condition is received, line finder is caused to hunt vertically until wipers reach a marked level. Vertical hunting is then stopped and horizontal hunt commences to find a particular marked contact in that level. It may be noted that in extreme case, line finder may have to take 20-steps -10 vertical and 10 horizontal -before a line is found. Line finders are made to step automatically, using interrupter contact mechanism. When line finder locates the subscriber line, start condition is removed, allotter switch steps on to the next free line finder in readiness for further calls and numerical selector sends out the dial tone to subscriber in readiness to receive dialling pulses. Thereafter establishment of the connection proceeds in usual manner.

Apparently, Design 3 is by far the best for a 100-line exchange. If we had used Uni-selectors as line finders, it would have been essential to divide subscriber's line into small groups of, say 24 each. Such designs involving groupings, functionefficiently only under certain specific traffic conditions and usually result in higher blocking probabilities.