A plumb level is the forerunner of the spirit level: a batten with a long, perfectly straight underside and a plumb bob hanging from the middle. If the line hangs exactly against the mark in the centre, the surface the batten is resting on is horizontal. In Dutch the tool is called a loodrei.
The principle is pure gravity: the plumb bob always points straight down. Tilt the batten and the line moves away from the mark. No vial, no laser and no battery is needed — which is why the instrument was used for centuries, from Egyptian and Roman building right into the nineteenth century.
Versions
- The standard model — the bob hangs through an opening exactly in the middle of the lower rail
- The extended model — the line continues below the rail, allowing a more accurate reading
- The flat model — a wide version resembling a straightedge, with the bob in a frame above the batten
- The A-frame — two legs forming a triangle with a cross rail carrying the centre mark
A version with the legs vertical, where the line runs along the side of the batten, checks the plumb of a wall instead.
Why the principle still matters
You mostly see the plumb level itself in restoration work and museum collections, but the logic behind it is still in daily use:
- A straightedge is worthless if it is not straight — a bent or dented batten always gives a false reading, vial or no vial
- Measuring longer means measuring more accurately — a short level on a long wall magnifies every error. Put a short level on a long straightedge instead
- Check your own tool — take a reading, turn the level end for end and read again. If it now shows something different, the tool is out of adjustment
- Gravity does not lie — even alongside a laser, a plumb bob is still the quickest way to check the vertical of a stud or frame
Related terms
- Plumb bob
- Spirit level
- Walking line
- Facade
- Window frame
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