A <a href="https://en.wikipedia.org/wiki/Rotary_dial" class="extiw" title="wikipedia:Rotary dial">rotary dial</a>, used for <a href="https://en.wikipedia.org/wiki/Pulse_dialing" class="extiw" title="wikipedia:Pulse dialing">pulse dialing</a> seen from the back while dialing. Two LEDs have been attached, to show the two switches the dial operates. One (red LED) is normally open (NO), and is closed when the rotor is drawn back and remains closed until the rotor fully returns. The other (green LED) is normally closed (NC), and is opened briefly to produce pulses. The number of pulses matches the number dialed (a single digit, 0-9).
This dial was purchased in 2011 at the MIT flea market, in Cambridge, MA, USA.
<a href="//commons.wikimedia.org/wiki/User:Naib" title="User:Naib">Mark Fickett</a>
CC BY 3.0
<span class="int-own-work" lang="en">Own work</span>