Rotary Dials vs Key Pads
Phone key pads are actually a somewhat recent invention.
Until the 1970's, the rotary dial was in widespread use. Numbers
were dialed by turning and then releasing a disk on the front of
the phone. When the disk was released, a spring mechanism inside
the phone returned the disk to its original position while generating
a certain number of pulses at the proper rate.
Since then, rotary dial phones have largely been replaced by touch
dial phones which have calculator-like keypads. To dial a number,
simply press the buttons with the corresponding digits. The phone
then sends the corresponding DTMF tones to
the phone company. Note that most phones can be set to send
pulse dial signals instead.
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