This is a volvelle-type (wheel & window) combat result chart for Swords & Wizardry.
Heres how my mind works—When I think of 1974, there is one tool that epitimized nerds more then anything else—the Slide Rule. Its an amazing piece of technology that was pretty much killed off by the pocket calculator, and later the PC. But looking at the attack roll charts in S&W, I had the thought – "I bet I can make a sliderule type tool to make that easier."
So after a few nights puttering around I came up with this volvelle design. Pretty simple—you cut out the two circles, and pin them together through their center—and then just line up your character's level with the target's AC. Pretty simple.