A protractor is an instrument used for measuring angles. This protractor (circa 1800) is made of brass and has a scale below it that can be used with a pair of compasses to measure 1/10th and 1/100th of an inch.
<a href="//commons.wikimedia.org/wiki/User:Compo" title="User:Compo">Compo</a>
<span class="int-own-work" lang="en">Own work</span>