Now with the 4 most popular scales: EC, CF, 500:1 ppm, and 700:1 ppm! The E.C. Dipstick™ dissolved salts pen operates on 3 common inexpensive AA alkaline batteries. Measures in PPM, EC and CF scales. There is no calibration required. It calibrates itself each time you replace the batteries. The EC Dipstick™ is waterproof to one meter.