The Level

Level and plumb are the two reference lines of all building: horizontal and vertical. Every wall, floor, pipe slope and tower depends on them.

Water and gravity

The first levels relied on gravity through a plumb bob or on water's tendency to find its own level. Egyptian builders used A-frame levels with plumb lines. Roman engineers leveled aqueduct gradients over long distances with the chorobates, described by Vitruvius. A clear hose filled with water, a "water level", is still used to transfer a level mark around corners and through rooms.

The spirit level

In 1661 the French scientist Melchisédech Thévenot described a sealed glass vial filled with alcohol and containing a bubble. When the bubble centers between marks, the vial is level. Set into a straightedge, the vial became the carpenter's level; a second vial set crosswise reads plumb.

Levels across a site

To carry a level over a building site, builders use a telescope on a tripod: the builder's level, the transit, and the modern automatic level. A rod held at each point gives its elevation relative to a benchmark. This is where carpentry meets surveying.

Lasers

Rotating lasers sweep a level plane through a room or site. Receivers on grading machines use it to cut and fill automatically, a system called machine control. In a tower, lasers and total stations transfer control lines up through the floors so every column stays plumb.

Checking a level

A level can be wrong. Read it, flip it end for end, and read it again at the same spot. If the bubble does not match, the level needs adjustment. It is the first lesson in trusting instruments: check them.