To ensure ongoing accuracy, you should calibrate your pH pen on a regular basis. Calibration is a two-step process. First, clean your pH pen and then calibrate to two pH points using Bluelab pH buffer solutions (pH 4.0 and 7.0). The on-screen information will guide you through the process. Once complete, the calibration symbol will appear on your screen. You should recalibrate whenever the calibration symbol disappears or after cleaning your pen. If you take daily measurements, you'll need to calibrate more frequently. Conductivity pens are factory calibrated and won't need further calibration; however, you should clean your pen regularly. Instead, you should clean your Bluelab EC probe and then use Bluelab 2.77 EC Conductivity Standard Solution - 500 ml to check that cleaning has been successful.