The level and pendulum (plumb) bob are common tools used in building and surveying since ancient times. Levels determine the horizon. Plumb bobs, originally made of lead, work with gravity to ensure buildings are vertical. As cathedrals and early skyscrapers moved towards the heavens, plumb bobs were hung above brass datums fixed in the floor, many of which remain inlaid in floors today. The most ancient pictographs of all societies show some variation of the plumb bob, whose cord aligns with the vertical. Historical re-enactment experiments have shown that the highly accurate alignments of ancient structures, from monuments like Stonehenge to the great pyramids, are readily achievable with only this simple device and the geometric mathematics that accompanies it. Water or spirit levels, simple bowls that allow the liquid to settle into its natural configuration, often substituted for the bob. Until the recent development and marketing of laser leveling devices, these simple and ubiquitous tools have remained virtually unchanged. Even today, they are found in the toolbox of every carpenter, builder, or craftsperson. Set in motion as a pendulum, they became timekeeping devices and regulators. With delicate adjustment and measurement, they were even used to detect and measure the attraction of mountains, and refine the gravitational constant. Only in the nineteenth century was definitive proof of the earth's rotation achieved, thanks to observing the motion of the Foucault pendulum.