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
π SKIL 24-Inch Digital Level - LV941901
8 Review
DigiPas DWL80PRO: Compact Digital Level & Angle Gauge - Accurate Protractor, Bevel Gauge, and Angle Finder, 0.05Β° Sensitivity, 4 inch Pocket Size
11 Review
Johnson Level & Tool 40-0912 Self-Leveling Cross-Line Laser Level, Red, 6 x 7 Inches
10 Review
Kapro 307-08-TMS Try And Mitre Layout And Marking Square With Stainless Steel Blade, 8-Inch Length
18 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
Triangle Group TR918 225/45 R18 95V summer
61 Review