Milwaukee MW500 LED Economy Portable ORP Meter with Platinum Electrode, +/-1000mV, 1mV Resolution, +/-5mV Accuracy is simple and convenient to use. Use and Care : Properly maintaining your ORP probe will give you fast, accurate results for longer. Here are our top three tips : 1. Always store with the cap full of buffer or storage solution not water. 2. Clean your probe regularly by soaking in cleaning solution. 3. Calibrate after cleaning and/or storage before testing to adjust for changes in the ORP probe sensor.