The Myron L Ultrapen PT5 is designed to be extremely accurate, fast, and simple to use in professional water analysis. The PT5 Ultrapen is a true one-handed instrument, measuring dissolved oxygen concentrations in ppm, Saturation in percentages and temperature. The PT5 offers dynamic membrane temperature correction, adjusts for altitude and salinity, and features three calibration methods (air, water, and 0 ppm dissolved oxygen). The waterproof tester pen has a rugged, aircraft aluminum body that ensures excellent durability. Made in the USA.