With its super tough, high quality, fully waterproof design, no calibration required, daylight readable blue LED's and no on/off buttons to worry about, the Bluelab Truncheon? Nutrient Meter has proven itself as the world's favorite nutrient meter. It is powered by three standard AA batteries. EC (0.2 – 3.6), CF (2 – 36) and ppm scales (TDS and 700 scale). Fully waterproof design. No calibration required. Auto sense on and off. No external switches or adjustable buttons. Meter length: 40.7 cm or 16-1/32 in.