1. Immerse the test pen electrode in a mixed phosphate standard buffer with a pH value of 6.86 (at 25°C), and shake it gently;
2. Use a small screwdriver to adjust the calibration potentiometer until the displayed value matches the pH value of the standard buffer solution at ambient temperature;
3. The electrode is inserted into the PH4.01 potassium hydrogen phosphate or borax standard buffer solution of PH9.18;
4. The displayed value should be within the allowable error range compared with the pH value of the buffer solution.
