In order to guarantee the accuracy of your readings, it is necessary to bracket the expected pH values with at least two buffers. For example, if the sample is usually close to a pH of 8.00, then you will want to at least calibrate in pH 7.00 and pH 10.00 buffer. If you are expecting the pH to be in both the acidic and basic ranges, then a three-point calibration should be used.
Onset brands
