We love building things that make our lives easier, from the RECO resistor cutting robot that measures out and slices ribbons of resistors to the ICSQ Integrated Circuit Squisher, if we can put something together that shaves a few minutes off our day we'll gladly spend weeks perfecting it.
We're not alone, of course, and Instructable user Caspar has uploaded a neat trick for recycling an old or worn 12-inch ruler: building a drill bit gauge. Designed to help you quickly distinguish a 1.5mm drill bit from a 1.6mm drill bit, or any other sizes, a traditional drill bit gauge is made by drilling holes of varying size into a lump of wood, plastic, or metal. It's a system that works, but it's pretty time consuming: you need to drill a fresh hole for each size you want to measure, and make sure you do so cleanly with no wobble and label everything neatly.
Caspar's drill bit gauge, by contrast, comes pre-labelled. Taking a 12" metal ruler showing inches and tenths and cutting it in half, then gluing the two halves into a clapperboard-like arrangement, Caspar's creation uses the already-present markings to read off drill bit sizes: simply insert your bit and slide it from right to left, and wherever it comes to rest is the size in millimetres.
As well as working for a wider range of sizes than a traditional hole-based gauge, Caspar's creation requires no lengthy drilling or even pre-measurement: simply grab a 1mm drill bit and place it at the 1" mark then place a 5mm drill bit at the 5" mark before gluing the ruler pieces into place; everything in-between will naturally fall into place along the resulting angle. (You may, of course, need a separate drill bit gauge to find your 1mm and 5mm drill bits first...)
If that seems like magic - and, frankly, using inches markings to read millimetres strikes us as the darkest of dark magics - you can see the device in full on Caspar's Instructables page.
I made this a few years ago, and use it often. As my eyes age, this gauge makes selecting a drill from an assorted collection of odd sizes easy.