Two-Point Calibration
A two-point calibration is a more accurate calibration technique than the one-point calibration. The two-point calibration adjusts the meter at two different pH values, thus the meter has been adjusted so that its response is accurate at more than one point along the linear equation. The second calibration point is selected on the basis of the type of solution (acidic or basic) to be measured so that the linear response can be established.
When measuring acidic solutions, use a buffer that is acidic, pH < 7 (a pH = 4.00 solution is common). When measuring basic solutions, use a buffer that is slightly basic, pH > 7 (a pH = 10.00 solution is common).