Levels with a plumb down point (nadir)

Dot (nadir)

— point projection pointing vertically downward (nadir direction).

By itself, such a projection can be used, in particular, for making holes on the same vertical in ceilings located at different levels. It is enough to make one of the holes, install a level above it — and the laser beam going vertically downwards will indicate the location of the next holes. And in devices that also have a zenith function, marks from the zenith and nadir projections are located strictly one above the other. This is very convenient when marking the floor and ceiling at the same time for racks, partitions, etc.