Bluelab EC PenBLUELAB EC PEN The Bluelab EC Pen is a small, easy to use tool for measuring conductivity and temperature. It simply tells you whether your plants are getting the right amount of nutrients in your solution and whether adjustments are needed. Combine the Bluelab EC Pen and the Bluelab pH Pen to create a handy, convenient, and accurate system for ensuring optimal plant growth and health. Display options available in C, F, EC, CF, ppm 500 and ppm 700.