What Is a Dual-Grade Rotary Laser? Slope and Fall Explained

A standard rotary laser projects a perfectly flat, level plane. That's exactly what you want for foundations and floors — but plenty of groundworks jobs need the opposite: a controlled fall. Drainage runs, driveways, patios, ramps and car parks all have to slope by a set amount. That's where a dual-grade rotary laser comes in.

Single-grade vs dual-grade

A single-grade laser can tilt its plane along one axis — so it falls in one direction. A dual-grade laser can set an independent slope on two axes at once (often labelled X and Y). That means you can run a fall in two directions simultaneously — for example, a car park that drains toward one corner. Both the Grettz G70 and the green-beam G80 are dual-grade.

How grade is expressed

Falls are usually given as a percentage or a ratio. A 2% grade drops 20 mm every metre; a 1:40 fall (common for drainage) drops 25 mm per metre. On a dual-grade laser you dial the required percentage into each axis and the head tilts the beam to match.

Setting a fall in practice

1. Set up the laser over your high point and let it self-level.
2. Enter the required grade on the relevant axis — say 2%.
3. Use a staff and receiver to check the drop at each point down the run. The beam now falls at your set gradient, so the receiver reads on-grade along the intended slope rather than dead level.

Do you need dual-grade?

If your work is mostly flat levelling — floors, footings, general setting out — a standard rotary like the G60 is all you need. If you regularly set drainage falls, ramps or crossfalls, a dual-grade model pays for itself in time saved and re-work avoided. Compare the options in the rotary laser range.

New to rotary lasers generally? Start with our step-by-step guide to using a rotary laser.