[dagskarlsen]

The rotary dial has 5 wires, when the dial is moved out of the rest position 2 of these short out the receiver (loudspeaker) to eliminate noise. 2 of the 3 others shorts out the transmitter (microphone) to protect it from damage, The third is connected to the 2 others until the dial returns, when it returns it sends out small breakes (pulses) on the line to tell the exchange what number it dials, these pulses must be of a pretty accurate timing to work OK. A 0 gives 10 breakes of approx 67 milliseconds with approx 33 milliseconds between during a time of 1 second. when a 5 is only 5 of those pulses etc.

When the dial is in rest position you should have the dial tone.