Tajima/$30 and $40
Calculating rise over run isn't like horseshoes and hand grenades—close won't hack it. With Tajima’s slant tool, you don’t even have to calculate. Instead, you just directly measure the angle with a quick check and a turn of your thumb.
Five amazing, clean technologies that will set us free, in this month's energy-focused issue. Also: how to build a better bomb detector, the robotic toys that are raising your children, a human catapult, the world's smallest arcade, and much more.