Laser Levels with No Slopes

A self-levelling laser level without a grade function is a rotary laser producing a horizontal reference plane, some models a vertical one too, with no mechanism for tilting the beam. The compensator finds level automatically within roughly ±5° and holds an accuracy in the order of ±1–3 mm at 30 m; on most models, knocking the tripod makes the head flag the deviation and stop rotating. Dropping the grade function lowers the price and the number of settings an operator can get wrong, while levelling accuracy stays the same — hence the default choice where every reference point sits on one elevation.

A fixed-plane laser level covers tasks where points share one elevation: setting out strip and pad foundations, checking formwork heights, marking datum points before a screed pour, verifying floor flatness, and installing suspended ceilings, partition framing and soffit services. With a working radius in the order of 400–600 m using a detector, one tripod position serves a typical plot or a warehouse of several thousand square metres. Gradients for roads, ramps and sewer runs are the one thing it cannot do — those need a grade function.

Setting out a fall with a fixed-plane instrument means working around it, because the reference plane always stays horizontal. The gradient comes from the rod readings instead: for 1% the detector moves 10 cm down the rod for every 10 m of run, and pegs go in a few metres at a time. That works over short stretches — a terrace, a driveway, a screed fall towards a gully — but on roads, ramps and sewer runs it is slow and the errors accumulate. Those jobs call for a grade model, where the slope is keyed in on the panel.

The standard field check uses two instrument positions. Set the laser midway along a run of about 30 m between two grade rods, read the height on each with the detector, note the difference. Then move the tripod a few metres beyond one rod, repeat both readings and compare the differences. A discrepancy larger than roughly 3 mm at 30 m points to a compensator out of adjustment and sends the unit to service. Repeat the test every few weeks of use, and always after a drop.