HI-719-11 is a high-quality set of calibration standards that allows users to validate the Magnesium Hardness Checker®HC – HI-719. The HI-719-11 includes one sealed cuvette for zero ppm CaCO3 and one cuvette that is tinted to an equivalent 1.00 ± 0.20 ppm CaCO3sample @ 25°C. The calibration check set is produced using reagent grade chemicals in a temperature controlled environment.