I can understand to calibrate for a pH of 7 but cannot understand why use a buffer solution of pH 4! I'm sure one only needs to calibrate the meter at pH 7 and it's done!
So, some pH meters allow you to do a single point calibration but it is not as accurate. To get the best accuracy, you should do a 2, or even 3, point calibration as it essentially gives the meter more reference points to work from. In wine, we are measuring something acidic, so we use pH 7 and 4
@@PeterPete Most instruments are calibrated with one, or two, or three buffer solutions. If high-precision measurement results are required, calibrate with three buffer solutions.
@@PeterPete The device only receives a signal from the electrode. He must "read" the signal correctly. During calibration, the device "learns to read the signal correctly".