With its super tough, high-quality, fully waterproof design, no calibration required, daylight readable blue LEDs 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 (02?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: 40.7cm or 16 1/32in. 5 year Bluelab? Guarantee.