Which statement about calibration frequency is correct?

• A. pH meters require daily calibration.
• B. Conductivity meters require daily calibration.
• C. Calibration for pH meters and conductivity meters should occur on a scheduled basis, not necessarily daily.
• D. Both pH meters and conductivity meters should be calibrated daily.

Answer: (D)

Calibration frequency is about keeping measurements trustworthy by countering drift in the instrument over time. For pH meters, the glass electrode and reference junction are prone to drift from aging, fouling, and temperature effects. Calibrating daily with standard buffer solutions resets the instrument to known reference points, helping to ensure pH readings stay accurate for the samples you’re testing. For conductivity meters, the sensing cell and temperature compensation can also drift with use, fouling, or changes in the cell constant. Daily calibration with standard conductivity solutions (and appropriate temperature control) keeps the readings reliable and comparable from day to day. In many lab practices, setting a daily calibration baseline for both instruments helps protect data quality, consistency, and regulatory compliance, which is why this answer is considered correct.