Professional level, based correction, using an aluminum profile. Section 60x23 mm. Thickness 2 mm. The increased size and the internal reinforcement structure to prevent twisting. Masterlevel has side impact resistant caps. The vials are in a single block of methacrylate, which make it very clear vision while assuring extreme robustness to shocks. Accuracy of central vial 0.5 mm / m. The painting of an innovative structure makes aluminum slip.