steel ball bearings. These balls naturally roll to the lowest point, making it easier to identify true level from different viewing angles. In certain designs, three balls were used together to provide a clearer and more precise reading.
These unique tubes are often found in vintage tools made of wood, brass, or cast iron. They were commonly used by machinists and engineers who required high precision before the age of digital instruments.
While these glass tubes are generally safe if intact, the liquid inside can be flammable or toxic, such
