If the pH electrode is dry, soak it in tap water for 5 minutes. Add pH 7 buffer solution to a small beaker or vial up to a depth of 1/2 inch. Immerse the electrode in the sample of pH 7 buffer and allow the reading to stabilize. Use a small screwdriver to adjust the pH 7 calibration screw at the top of the meter until the display reads 7.00. Rinse the electrode with distilled water. Add pH 4 buffer solution to a different small beaker or vial and immerse the electrode in the sample. Allow the reading to stabilize. Use the small screwdriver to adjust the pH 4/10 calibration screw until the display reads 4.00.