Make Your Own 1952 Fraction-Of-An-Inch Adding Machine

"Evil Mad Scientist Laboratories writes -

Last weekend we took a trip to Urban Ore in Berkeley, where I found an incredible gem: this "Fraction of an Inch Adding Machine." It's a simple to use device that lets you add any number of fractions-- from 1/64 to 63/64-- quickly, automatically, correctly, and without thinking about it."

More Here (Including PDF pattern to make your own): MAKE: Blog: Make your own 1952 Fraction-of-an-inch adding machine