Straight Talk about Levels
DEAR TIM: My carpenter's level doesn't seem to be working right. The bubbles in the vials don't seem to read the same when you rotate the level. Is there an easy way to test mine? If I buy a new one what should I look for? What kind do you use? G. U.
DEAR G. U.: Your level may be perfectly fine. Do you remember dropping it recently? One of the endcaps may have shifted. You may have created an undetected high spot at one end of the level. Also check to see if the edges of the level are smooth. A piece of dried mud, glue, caulk, etc. may be creating your error.
If you can't find the problem, you can make a copy of an ancient Egyptian level. They made accurate levels by creating a simple A frame using a perfectly straight, horizontal brace or bottom member. A plumb bob was suspended from the apex of the A frame to the bottom brace. The clever builders then marked a point just below the bob while the horizontal brace was parallel with a small stationary body of water. From then on whenever they set this contraption on a surface and the plumb bob lined up with the mark, the surface was level!
However, before you go to that trouble let's do a quick test of your existing level. We need two 1 inch long flat head wood screws, a hammer, and a screwdriver. Find a nearly horizontal rigid piece of wood. This might be a beam, a foundation sill plate, etc. Hammer the screws into the wood about one half inch. I would like the distance between the screws to be 2 inches less than the length of your level.
Place the level on the screws. Adjust one screw until the bubble in the vial is perfectly centered. Rotate the level 180 degrees keeping the same bottom edge on the screws. If the bubble remains centered in the vial, this edge and its vial are OK. If the bubble shifts, the level is off by one half the difference of the bubble's shift. Flip the level over and check the other edge in the same fashion. You can do the exact same procedure using a vertical surface to check the plumb vials.
If your level happens to be a high quality one, the test will be easy. High quality levels have extremely well made and calibrated bubble vials. The edges of the bubble will just kiss the lines on the vial. You will not have to wonder when the bubble is centered. Lesser quality vials often require you to guess. These are the ones where the bubble is smaller or larger than the distance between the two lines. If you decide to purchase a new level, pay attention to the bubble vial's sensitivity. A good level has high sensitivity. Its bubble will move more quickly as the angle of the level is changed.
I happen to own wooden levels. Mahogany levels are usually very stable and have excellent weight distribution characteristics. I look for levels that have glass windows protecting the vials. Glass is more scratch resistant than plastic.
If you want a really nifty level, why not consider an electronic one? Some of these levels combine traditional bubble vials and electronic wizardry to take the guesswork out of making something level or plumb. The electronic window tells you degrees of angle, slope in percent, and even inches per foot. With these tools any DIY'r can easily run with the big dog carpenters!