Nomogram for calculating 1/x + 1/y = 1/z. The red line shows the calculation with x = 42, y = 56 and z = 24
<a href="//commons.wikimedia.org/wiki/Special:Contributions/134.34.142.193" title="Special:Contributions/134.34.142.193">134.34.142.193</a>
<span class="int-own-work" lang="en">Own work</span>