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 SKIL 24-Inch Digital Level - LV941901
8 Review
π 60MM High Precision Horizontal Bubble Cardan Level for Accurate Measurements
9 Review
Laser level HiLDA 4D/16 set 4
44 Review
DigiPas DWL80PRO: Compact Digital Level & Angle Gauge - Accurate Protractor, Bevel Gauge, and Angle Finder, 0.05Β° Sensitivity, 4 inch Pocket Size
11 Review
TV bracket Kromax DIX-18 black
52 Review
Kapro 307-08-TMS Try And Mitre Layout And Marking Square With Stainless Steel Blade, 8-Inch Length
18 Review
β Stainless Steel L-Square, Size 3-Inch x 4-Inch, Zona 37-434
8 Review
π CAMWAY 6 Inch Digital Caliper with LCD Display, Electronic Vernier Caliper, 150mm Stainless Steel Feeler Gauge, Plastic Digital Caliper Set for Zero Setting Inside/Outside Diameter, Depth, and Step Measurement Tool
3 Review