Back of a <a href="https://en.wikipedia.org/wiki/Rotary_dial" class="extiw" title="wikipedia:Rotary dial">rotary dial</a>.
<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>