Bluelab Truncheon MeterMinimum order quantity of this product: 3 quantity 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