
Although they might work sometimes. . The seams of the bubbles will get stuck or the glass in the plastic is NOT flat so you can count on it. Instead, I used a self-leveling laser. The laser hit the string straight and I didn't look back.

π Kapro 905-41-24 24-Inch Level Tool - Premium Bubble Level with Shockproof End Caps, Superior Accuracy & Visibility, Optivision Red and Plumb Site Dual View Vial, Condor Spirit Level
10 Review

Johnson Level & Tool 40-0912 Self-Leveling Cross-Line Laser Level, Red, 6 x 7 Inches
10 Review

Kapro 905 Condor - Professional Magnetic Box Level + High Contrast OPTIVISION Red Vial - 24
23 Review

π SKIL 24-Inch Digital Level - LV941901
8 Review

Triangle Group TR918 225/45 R18 95V summer
61 Review

β Stainless Steel L-Square, Size 3-Inch x 4-Inch, Zona 37-434
8 Review

π² Johnson RAS-1B Johnny Square: Professional Aluminum Rafter Square, 7'', Silver - Top Quality with 1 Square
8 Review

π Johnson Level and Tool 400EM-S 12-Inch Heavy Duty Metal Combination Square for Professionals, with Inch/Metric Measurements, Silver - 1 Square
8 Review