The Original Bluelab Truncheon PH Meter - 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. If the conductivity reading is too low, your plants may not be getting enough nutrients. If the conductivity reading is too high, plants can dehydrate. Understanding the conductivity of the nutrient solution takes the guesswork out of feeding plants. It will also save you money! Using the Bluelab Truncheon nutrient meter is the fastest and easiest way to measure the conductivity! To take a reading of your solution - simply place the probe head into the solution and the reading is indicated by the flashing lights. Calibration of the Bluelab Truncheon® PH Meter is not required.