Bullseye Bubble Level
2-axis bubble level
One of the most ingenious (and simple!) tools ever devised by man–purely in my personal opinion, of course — is the Bullseye Bubble Level ($3), or what I call a 2-axis bubble level.
This tool is used to level flat surfaces in two dimensions, parallel to the floor. For example, you would use this tool to level a kitchen cooktop, or a washing machine, or your workbench, or whatever. Just place the Bullseye Bubble Level in the center of the surface, then adjust the surface accordingly until the bubble is centered in the circle at the top of the tool.
It should be noted that you can achieve the same result (i.e. a level surface) using a standard bubble level. One simply places the bubble level along the diagonal of two opposing corners and then adjusts the surface accordingly; then rotate the level 90-degrees so that it is in line with the other set of opposing corners and adjust the surface in that direction. But why go through a two-step process (which usually ends up having to be tweaked and redone a few times) when all you have to do is place a Bullseye Bubble Level in the center and remove any guesswork, seeing “the whole picture” as you make your adjustments?
Like any tool, Bullseye Bubble Levels come in a wide range of styles, quality, and price; but even the most expensive model can be had for under $20. The Starrett Bullseye Bubble Level that I use, for example, is under $4! Yes, I said “Starrett” for under $4. And use it I do. You don’t realize just how useful this tool is until you actually own one. It’s great for leveling jigs and workpieces in a bench vise, for example. Ingenious, simple, useful, and dirt cheap. If that’s not a Cool Tool, then I don’t know what is!12/3/18