Model of a Chinese <a href="https://en.wikipedia.org/wiki/South_Pointing_Chariot" class="extiw" title="en:South Pointing Chariot">South Pointing Chariot</a>, an early navigational device using a <a href="https://en.wikipedia.org/wiki/Differential_(mechanical_device)" class="extiw" title="en:Differential (mechanical device)">differential gear</a>.
<a href="//commons.wikimedia.org/wiki/User:Andy_Dingley" title="User:Andy Dingley">Andy Dingley</a>
CC BY 3.0
<span class="int-own-work" lang="en">Own work</span>