This high precision hydrometer are handmade in Germany by experienced craftsmen. It have a maximum deviation of 0.0005. The hydrometer never need calibration. Indispensable for scientists and the committed hobbyist. The higher price will soon pay off by an always exact salinity in the aquarium. Scale from 1.018 to 1.028, with a marked recommendation range 1.021 to 1.024.Do you have questions about this article ?