Checking the Accuracy of a Spirit Level
A spirit level is designed to be robust for use on site but it is still a precision measuring instrument, which should not be abused or misused. It should not be dropped on to a hard surface, and hitting it with a trowel to adjust bricks that are out of level or plumb is bad practice and the sign of a poor bricklayer.
A good-quality spirit level comes with a vial that can be adjusted and all spirit levels should be checked from time to time for accuracy, if the quality of the brickwork on which it is used is to be maintained. The obvious method is to check the device against a surface that is known to be level and/or plumb but often this is not possible or completely reliable. The following method is a good alternative (see Fig 66):
Fig. 66 Checking spirit levels for accuracy.
1. Insert two screws in a generally level surface a distance apart just less than the length of the level.
2. Place the level on top of the screws and adjust one of the screws until a level reading is obtained.
3. Turn the level through 180 degrees and note the new reading. If the reading still shows level then no adjustment of the vial is necessary. If, however, the reading shows an error, half the error should be corrected by adjusting the vial and half by adjusting the screws.
4. Turn the level through 180 degrees again. It should now read accurately in both directions.
The same method can be used to check accuracy for plumb, by using two screws fixed into a generally vertical surface.