You may have come across tiny glass cylinders containing three small metal balls inside. These aren’t random odds and ends—they’re precision parts from antique leveling instruments, commonly known as bullseye or machinist’s levels. 
What They AreUnlike traditional carpenter’s levels that use a single air bubble inside a curved vial, bullseye levels have a circular, dome-like chamber filled with liquid, allowing them to measure level in multiple directions simultaneously. In certain older European or industrial designs, steel ball bearings were used instead of—or alongside—the standard bubble. The balls naturally roll to the lowest point, clearly indicating level from any viewing…
