It is essential when growing with a hydroponic solution to know what the strength of the solution is before feeding your plants and while they are growing. This is easy if you use the Bluelab truncheon nutrient meter to take a reading of your solution, simply place the probe head into the solution for 1-2 minutes to reach the same temperature of your nutrient. The reading is indicated by the flashing lights. Calibration of the meter is not required. Meter length: 40.7 cm (16 1/32 in). Features fully waterproof auto on/off function daylight readable blue leds battery operated no buttons, switches or knobs provided with ec, cf, ppm 700 and ppm 500 scales.