PH Buffer 4 is to calibrate your pH meter in order to make sure that you get the most accurate reading.
Using a pH Buffer 4 is simple:
Pour some of the pH Buffer into a small clean vessel and immerse the probe of the meter into the buffer.
Leave the meter for a few minutes and push the calibration button on the meter to set it to 4.0.
Your pH meter is now calibrated and ready to use again