From construction to engineering, plumbing to carpentry, spirit levels are vital tools used in numerous trades and industries. Designed to help the user gauge how parallel (level) or perpendicular (plumb), an object or surface is relative to the ground, these instruments usually comprise glass tubes - known as a vials - containing a liquid spirit like ethanol and an oxygen bubble, which sit inside a flat metal or plastic housing.

While good quality spirit levels are generally accurate, when you think about the worksite environment and rough and tumble they are typically subjected to, it becomes clear why it’s considered good practice to regularly check your level’s accuracy. The process of correcting potentially inaccurate readings is known as ‘calibrating’ and is simple to do.

In this post, we look at how to properly read your spirit level, how to know if the readings it is providing are accurate and how to go about calibrating if they are not.

How to read a spirit level

Reading a spirit level is simple. Typically, the vial on a level features two graduation marks that the bubble will sit perfectly between when the tool is placed on a flush surface. If the bubble moves and is found resting over or outside these graduation marks when placed on a surface, this indicates that the object you are testing is not level and adjustments to the surface are needed. When the right side of an object or surface is too high, the bubble will rest on the left side of the vial, and vice versa if the left side is raised.

 

How to check if a spirit level is accurate

The process of testing the accuracy of your spirit level and fixing it if needed is relatively quick and simple. While it may take a few tries to get used to what you are looking for, if you follow these seven basic steps, keeping your spirit level in fine working order can be a piece of cake.

1. Place your spirit level on a piece of paper and then sit both items on a surface that you believe to be flat - a sturdy table or a kitchen counter will work. Using a pencil, make two marks on the piece of paper - one at each end of the level.
2. Let it sit for 20 seconds to allow any vibrations to dissipate.
3. Next, note where the centre of the bubble rests inside the spirit vial. Use the graduation marks and any additional measurement markers printed on the outside of the vial.
4. Once you have noted down the location of the bubble, turn your level 180° and align it with the pencil marks you made earlier. Once again, wait 20 seconds and then note the new position of the bubble.
5. If the bubble sits in the dead centre of the two graduation marks on your level, then your level is calibrated correctly and no further action needs to be taken. However, if the bubble rests in a different position during either reading, you will need to continue to step six.
6. If the bubble doesn't sit in the centre, note which side of the vial the bubble drifts towards - either left or right - then flip back 180° and repeat. If the bubble drifts towards the same side in both readings, this indicates the surface you are using is not flush and you will need to find a new surface to test your level on and start again from step one. However, if the bubble shifts towards the opposite side of the vial during the second reading, this confirms your level is off and needs calibrating.
7. To fix this fault and calibrate your spirit level, you need to locate the calibration screw. This is likely to be found on one edge of the level, usually directly under the vial. Ensuring the tool is set on your flat surface, use a screwdriver to slowly turn the screw. You will notice that the bubble inside the vial will begin to move one way or the other. Simply turn the screw until the bubble rests in the dead centre of the vial. Once this has been achieved, repeat steps one to five to confirm that your level is now providing accurate readings