Special Offer! Buy both p H solutions for £2.99! All p H meters need to be calibrated on a regular basis. As time passes by & with regular use p H meters can lose their accuracy. To calibrate ensure the electrode is clean & dry & put it into a sachet of p H7 buffer & wait for about 30 seconds for the reading to settle. If the reading is outside of the range stated on the sachet use the screwdriver trimmer to adjust the display to read 7.01. If you store this sachet in a dry environment away from heat or cold you can use this sachet or buffer a few more times. Recalibration can be done once a week or if you use the p H meter less regularly calibrate before each usage. After calibration rinse the meter (without letting any water go above the max line) & shake to dry. The probe should be stored in p H4 Storage solution when not in use. Always rinse the p H4 Storage solution off before taking a reading.