Abstract: A portable gravity-based self-levelling device for projecting a laser ray or a flat beam of laser rays (L, L11, L12, L110, L120) in a horizontal and/or vertical direction even if the device lies in an inclined position, comprises: a case (C) in the form of a hollow housing (1); a pendulum (11) suspended inside the case (C) by suspension means (5, 9); means (23A, 23B, 24) for damping the pendulum swing; means (18, 19) for adjusting the equilibrium position of the pendulum (11); and, mounted on the pendulum (11), means (12) for projecting collimated visible laser rays. The suspension means comprise at least one first mechanical decoupling member such as a ball or roller bearing (5), associated with the hollow housing (1), and, lying in a plane perpendicular to that of the first member (5), a second mechanical decoupling member rigidly secured to the movable part (6) of said first member and supporting the pendulum (11).

Abstract: The projector device for laser rays (4) is mounted on an apparatus which oscillates and is self-leveling (2, 3, 5) under the force of gravity whereby in the equilibrium position a ray is projected on one or more walls always in a perfectly horizontal position. The oscillating apparatus is interrupted in its oscillations by a manual mechanical brake (6, 7, 8 and 9). The device can rotate and includes a graduated ringnut (11) on which it is possible to read the angle of rotation of the laser ray with respect to a predetermined reference point.