Extra-rigid rectangular aluminum profile with patented anti-knock protection for direct correction of deviations, building material is aligned with the anti-knock protection with light taps, no need to change tools, spirit level with a precisely milled measuring surface, no discoloration on surfaces, e.g. on exposed brickwork, always at eye level, the Second vertical spirit level offset in the middle enables easy reading in all measuring positions, reinforcement ribs for high stability and a secure grip when working, shock-absorbing, removable end caps, the two-component material mix protects the profile from impacts, easy to clean thanks to the electrostatic powder coating, STABILA Built-in technology ensures long-term precision, measurement accuracy in normal position ± 0.5 mmm, in reverse position ± 0.75 mmm, particularly suitable for masonry work, for example when setting a wall