Extendable spirit level with stable 3-chamber aluminum rectangular profile and extra-strong rare-earth magnet system for optimal adhesion to metallic components, hands free when aligning and adjusting posts and supports, extremely long measuring surface thanks to a unique telescopic system, strong eccentric clamps for permanent measuring accuracy, access openings for one secure hold when working, profile with reinforcement ribs for high stability, continuous bridge over horizontal spirit level also stabilizes the profile, plastic end caps protect the profile from impacts, telescopic rod with cmin scale, STABILA installation technology ensures long-term precision ? Measuring accuracy in the normal position (closed) ± 0.5 mmm, in the reverse position (closed) ± 0.75 mmm, the strong adhesive force of the rare earth magnets is particularly required in metal construction