Why Does a Bubble Level Have Extra Lines?

What are the extra lines on a bubble level actually for? Most of us use a level for one simple job: center the bubble and make sure a shelf is straight. But some vials have three lines on each side of the bubble. On levels designed to measure slope, those extra marks can help show a deliberate 1% or 2% incline. In this video, we look inside the tool, see why the bubble moves, and explain how the markings can help when a surface needs to guide water in a particular direction. Not every bubble level uses the same scale. Check the markings or instructions for your specific model before using its lines to measure slope. What everyday object should we investigate next? Tell us in the comments. SOURCES & FURTHER READING • Ebisu — How two-line, four-line and six-line vials are read: https://www.ebisu-level.co.jp/eng/lev... • Shinwa — How to read a level designed for 1% and 2% slopes: https://www.shinwasokutei.co.jp/featu... • STABILA — Example of a six-ring vial designed for 1% and 2% slope measurement: https://www.stabila.com/en/products/d... • Johnson Level — How the bubble and the vial work: https://www.johnsonlevel.com/News/Lev...