The ruler is quite simple. A sawed-off, unentgratetes aluminum profile with grip. The dragonflies are likely only a rough guide. Vertical it deviates by approx 10mm / m; Horizontal approx 4mm / m. The scale starts not quite one hundred percent at 0. Does zero is approx 0.5-1mm offset to the right. With Caliper I have not measured it precisely. Conclusion: It corresponds to halt its Preis.Wer not have to work on NEN millimeter, or even have a real bubble level to take, for it is ok