A great all around meter for nutrient applications needing constant monitoring. It measures PPM, pH and Temperature. Its large illuminated green LCD display allows easy reading from a distance. Both pH and PPM are temperature compensated for accurate readings. The electrodes are replaceable. Calibration screws are conveniently located on the front for easy access. The chip is programmed to use the international water standard 500 PPM = 1 EC TDS measurement. It uses a standard 120 volt AC current to low voltage DC power supply. The 24-7 Nutrient Monitor comes with 4voz bottles of 1382 PPM, pH 4.0 and pH 7.0 calibration solutions.