EC measurement meters such as the EC-1200 and EP-1400 meters from Nieuwkoop need calibration on a frequent basis. These pre mixed calibration fluids help you to do proper calibration. It is preferred to use the Nieuwkoop calibration station to ease the job of calibration. Do not polute your stock bottle by inserting the sensor to calibrate directly in the bottle. Pour a small quantity in a small cup and do calibration from there, after calibration dispose the used liquid