Does the pH meter need to be calibrated before each use?
No, most pH meters hold calibration very well. If you are using your meter every day then check it once a week. If you get a reading that is above or below what you were expecting, then check the measurement of one of the standards, either pH 4.0 or 7.0 and observe what the meter shows for the value compared to the known value of the specific standard. Recalibrate if you observe that the reading is different by 0.2 pH units or more.
