Hanna pH 4 Calibration Solution 20 ml. x 25 units

In case of manual calibration with PH4 buffer on 20ml, turn on your meter, place the meter or electrode into the beaker, stir gently to facilitate the meter's reading of the buffer, and, with the help of the calibration screwdriver or the calibration wheel (depending on the model), adjust the reading on your display to the value indicated on the buffer.