Milwaukee C66 Waterproof High Range Conductivity Pen with ATC and Replaceable Electrode

SKU: C66
Accuracy: EC: ±2% Full Scale
Temperature Compensation: Automatic
Range: 0.00 to 10.00 mS/cm
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The Milwaukee Conductivity Pen is designed for hydroponic and other growers to help you make sure that your plants are receiving the right amount of nutrient. Keep EC in your target range to help your achieve better results.


  • Measures conductivity and temperature with automatic temperature compensation
  • Ideal range for hydroponics (0.00 to 10.00 mS/cm)
  • Units in mS/cm easily convertable to ppm
  • Factory calibrated with the ability to recalibrate if needed
  • Replaceable electrode
  • Fully waterproof to IP65
  • 250 hours continuous use (3 x 1.5V batteries included)



EC electrodes can develop nutrient build up over time. To miminize build up, always rinse the probe in fresh tap water after every use.


The Milwaukee EC Pen, like all conductivity meters, provides a measure of electrically charged ions in a solution and is an absolute measure of conductivity.
EC is often converted to TDS in parts per million (ppm). Different scales include the 500 scale, 650 scale and the 700 scale. However, true PPM can only be determined through chemical analysis.
Your mS/cm reading can be approximately converted to TDS (ppm) as shown in the examples below.
2.00 mS/cm = 2000 uS/cm = 1000 ppm on .50 factor scale
2.00 mS/cm = 2000 uS/cm = 1400 ppm on the 442 scale or .70 factor scale
Thank you for considering Milwaukee to help you take your results to the next level.


Range: 0.00 to 10.00 mS/cm
Resolution: 0.01 mS/cm
Accuracy: ±2% Full Scale
Typical EMC Deviation: ±2% Full Scale
Temperature Compensation: Automatic from 5 to 50°C, with ß=2%/°C
Calibration: Manual, at 1 point through trimmer
Probe: MA73076 (replaceable)
Environment: 0 to 50°C / 32 to 122°F; max RH 100%
Battery Type: 3 x 1.5V (included)
Battery Life: Approx. 250 hours of continuous use
Dimensions: 6.5 x 1.2 x 1.2 inches
Weight: 3.5 ounces

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