Levels & Squares

Level, plumb and square are the three things that cannot be eyeballed. An I-beam level is the jobsite standard because the shape resists twist, which is what actually throws a reading off over a long run. A magnetic edge frees both hands on conduit, strut and steel stud, and is the reason most electricians own a magnetic level rather than a plain one. Length is the real decision: a compact torpedo lives in a pouch and levels a box or a short run of pipe, a 24-inch spans most framing and panel work, and a 48-inch is what you want for a door, a rack, or anything where a short level would ride a local high spot and lie to you. A framing square handles the other axis - marking a true 90, laying out a cut, checking a corner that has to be right before anything gets fixed to it. Aluminum stays readable and does not rust in a truck. Check a level against itself by reversing it end to end; if the bubble moves, it is out.