EC PPM CF Nutrawand Hydroponic Meter Stick Measuring range:CF: 4~52CF / EC: 0.4~5.2EC / TDS: 280~3640ppm (EC x 700) / TDS: 200~2600ppm (EC x 500) Resolution: CF: 1CF; EC: 0.1EC; TDS: 70ppm (700 conversion factor); TDS: 50ppm (500 conversion factor) Accuracy: 4% of reading Automatic Temperature Compensation:0~50C (32~122F) Factory Pre-Calibrated