Confirm the level is true horzontal and vertical for accuracy and adjust for variances. It’s important to check the level on both the horizontal and vertical vials. If you suspect your level is not true, it’s best to get it calibrated or replaced. A true level is essential for accurate measurements and construction. Here are 3 ways to check:
1. Checking for vertical, also known as plumb. I install 2 screws 4’ apart on a wall, door jamb or stud and let them stick out 1/4” or so. Adjust one of the screws until the proper vial reads true, plumb. Then simply rotate the level, keeping the top the top and put it back against the two screws and take a reading. If the indicates that the level is still level 180° apart then you know your level is true for measuring plumb.
2. Place the level on a flat surface, sometimes I shim one end so it reads true. Then I rotate the level 180° keeping the tap the level still the top and if it’s still reads level, then you know that your level is true.
3. Sometimes I use another level that I already checked and is true and I can compare the two.