Keson LKTRF 9″ Rounded Torpedo Level
A bubble level (or “spirit level” in some circles) is an indispensable tool for builders and makers everywhere. There are some pretty large and expensive levels out there too, but most of the time, you'll do just fine with a one-handed torpedo level like the Keson LKTRF.
At 9 inches in length, LKTRF is a popular choice with plumbers and anyone else who often has to work in tight spaces. The rounded end allows it to get flush against walls with beveled corners, and the two “FOCUS” vials offers 20% magnification for more accurate readings.
Despite being quite lightweight, this level is super sturdily constructed so you don't have to worry about the body warping and thus affecting the tool's reliability.
Get the Keson LKTRF for $18 on Amazon. They also offer a straight-edge model (LKTSF).