All Mesa Laboratories Conductivity Calibrator Solutions are laboratory quality, NIST-traceable, standard solutions used for the calibration of conductivity meters. Tolerance: +/- 0.01 at 25° C Solution Specifications: Sodium Phosphate Dibasic (CAS # 7558-79-54)?Potassium Phosphate Monobasic (CAS # 7778-77-0)?Deionized Water (CAS # 7732-18-5)