Spirit level: how to hold it safely

Learn to hold and read a spirit level correctly so you can trust what it tells you.

SL-01Know the parts of a spirit levelA spirit level is a straight bar with one or more bubble vials - small liquid-filled tubes with a bubble inside. When the bubble sits exactly between the two lines on a vial, the surface is level (flat side-to-side) or plumb (perfectly upright). Most levels have one vial for level and a second one at right angles for plumb.

SL-02Hold the level flat against the surfacePlace the whole long edge of the level against the wall, shelf or surface you're checking - not just the ends. If the middle lifts away from a bowed or uneven surface without you noticing, you'll get a false reading. Take a moment to check the full edge is touching before you read anything.

SL-03Look straight at the bubble, not from an angleMove your head so your eye is level with the vial, looking straight at it face-on. Viewing the bubble from above or to the side makes it look off-centre even when the surface is fine - this is called parallax error. Always line your eye up dead centre with the vial before you decide what it's telling you.

SL-04Read a level (horizontal) checkWith the level held flat along the surface, watch the bubble in the horizontal vial. If it sits exactly between the two marked lines, the surface is level. If it drifts towards one end, that end is higher - adjust and check again until the bubble settles centrally.

SL-05Read a plumb (vertical) checkStand the level upright against a vertical surface, such as a door frame or a batten. Use the second vial, usually near one end, marked for plumb. The bubble should sit centred, which tells you the surface is perfectly upright with no lean either way.

SL-06Avoid the uneven pressure mistakeDon't press harder on one end of the level than the other - this tips it very slightly and skews the reading without you realising. Hold it with light, even pressure along its length, or better still, let it rest under its own weight against the surface.

SL-07Prove your reading by flipping the levelTurn the level end-for-end (180 degrees) on the same spot and read the bubble again. If it sits in the same place both times, your reading is accurate. If the two readings disagree, either the level is out of true or the surface is uneven - trust the flipped test over a single reading every time.

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