The Bluelab Truncheon measures the nutrient strength of a solution. It is essential when growing hydroponics to KNOW what the strength of the solution is before feeding your plants AND while they are growing.
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. Remove from the solution and place back in to take the reading as indicated by the flashing lights. Rinse the probe after use in fresh water and clean once a week to ensure the Truncheon remains accurate.