Wikimedia CommonsCool Facts
Bubble tells the truth. Inside a spirit level is a clear tube filled with colored alcohol and one air bubble. When the bubble sits exactly in the middle, you know your surface is perfectly level or plumb (perfectly vertical).
Why alcohol, not water. Builders use alcohol inside instead of water because it doesn't freeze in cold weather and moves more smoothly, which makes the bubble respond faster and more accurately.
Two different designs. Some spirit levels have a long tubular vial for checking if things are flat, while others have a round bull's eye vial for checking if poles or posts are standing straight up.
Used by many trades. Carpenters, bricklayers, stonemasons, and metalworkers all rely on spirit levels to make sure buildings and structures are built straight and true.
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