The MELAtest 60 has a conductivity sensor so the operator can check quality at any time. The quality is a direct depended upon the supply. To check the quality, dip the conductivity sensor into water. The conductivity will then be displayed after a few moments. Water that is poor quality contains impurites such as calcium and magnesium, which means that the color of the water may change or rust may appear. The calibration fluid MELAG Art. No. 55845 is recommended to calibrate the machine.