Why a Slide Rule Works
So I&#x27;ve known about slide-rules for a while.<p>What I didn&#x27;t realize was that the mechanical principles of slide-rules were applied to fire-control computers on WW2-era Battleships.<p><a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Mark_I_Fire_Control_Computer" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Mark_I_Fire_Control_Computer</a><p>These computers had slide-rule like cylinders that would rotate. As you aimed the gun sights &quot;at&quot; a target, the gun&#x27;s coordinates were being mapped to a cylinder, which would move the gun a different direction (you have to aim the gun &quot;higher&quot; the further away the target is, to account for gravity &quot;drooping&quot; the bullet).<p>In effect; the weirdly shaped cylinder inside the fire-control computer is a pre-computed solution that maps x&#x2F;y coordinate inputs to a z-coordinate output (where &quot;z&quot; would be fed into the gun&#x27;s raw aiming system).<p>The different parameters of the gun were programmed in with gears and cranks, moving the cylinder around physically.<p>For more details, see: <a href="https:&#x2F;&#x2F;www.youtube.com&#x2F;watch?v=gwf5mAlI7Ug" rel="nofollow">https:&#x2F;&#x2F;www.youtube.com&#x2F;watch?v=gwf5mAlI7Ug</a><p>Its a 20-minute video. The cylinder mechanism (of 2x inputs mapped to 1x output) is specifically talked about here: <a href="https:&#x2F;&#x2F;youtu.be&#x2F;gwf5mAlI7Ug?t=636" rel="nofollow">https:&#x2F;&#x2F;youtu.be&#x2F;gwf5mAlI7Ug?t=636</a> . Carefully crafted cylinders could be any pre-computed 2-input &#x2F; 1-output function.<p>---------<p>Mechanical computers are fun. Slide rules are but the simplest kind. People were using more complicated &quot;mechanical computers&quot; for very serious combat &#x2F; rangefinding &#x2F; etc. systems just a few decades ago, before the advent of modern digital computers.