Every workshop needs a level. Ideal for ensuring well-positioned wall hangings and perfectly upright posts, a level lets you know when you've achieved a horizontal plane. It does this through the use of an air bubble trapped in liquid and encased in a glass tube centered in a plastic, wooden or metal frame. Simply place the level on a surface and the air bubble can be measured against two static, vertical lines. If the air bubble is not perfectly centered between the vertical lines, the surface is not level [source: Encyclopaedia Britannica].
The most common levels come in 2-foot (61-centimeter) and 4-foot (122-centimeter) lengths, although longer levels are available, too. For durability (and aesthetics), steer clear of plastic versions; an aluminum or wood level should last a lifetime, particularly if you keep the wood well-oiled and store in a cool and dry place. Some level manufacturers offer replacement vials, should yours break, and this guarantee will be spelled out on the label [source: Carter].