A solution with a set EC value of 1.413 mS/cm to be used for calibration of EC meters, monitors and controllers. Most meters and controllers use EC Standard 2.76 but some meters such as the Aqua Master range require EC Standard 1.413. Use All meters require regular calibration for reading accuracy and to ensure the salts found within nutrient solutions is totally dissolved. Dependent on use, it is good practice to calibrate EC meters at least once a month to maintain accuracy.