For more than three millennia, builders have used levels to ensure the structures they were erecting were plumb vertically and horizontally. During that time frame, the tool has undergone four major transformations: from primitive mechanical levels to water levels, spirit levels, and electronic levels.

Primitive Levels
Historians say that the Egyptians were the first to use levels as far back as 1100 B.C. About one thousand years later, builders used an A-frame level, on which a plumb line was suspended from the vertex of the A. When the feet of the A were set on the surface to be checked, if the plumb line bisected the crossbar of the A, the surface was horizontal.

Water Levels
The first known use of such an instrument was by Italian astronomer Giovanni Riccioli in 1630. This instrument was a water filled tube with two glass cylinders, one on each end. When the water line in each cylinder was even, the surface to be leveled was horizontal.

Spirit Levels
Invented in 1661, the spirit level -- also called a bubble level -- initially featured a straight sealed glass tube containing water and an air bubble. However, the level underwent many refinements. First, the water was replaced by alcohol or other spirits to prevent freezing. Next, replacing the straight tube with a slightly bent one lessened the erratic movement of the bubble.

Electronic Levels
In the mid-1980's, battery-powered electronic levels first hit the market. In 1989, a digital level was introduced that lets users measure angles four ways: degrees, percent slope, pitch, and simulated bubble.