Growth Technology PH buffer 4 and 7 solutions are of a known and fixed PH, which are used to calibrate your PH meter and should be done on a regular basis to ensure ongoing accuracy from the meter. Pour out a small amount to use for calibration and remember to discard the used solution when finished, do not pour it back into the container as it will contaminate your new solution. First use PH buffer 7 solution to calibrate your meter to neutral, once this is done we recommend you then use PH buffer 4 to calibrate your meter to this level, this will give you a two point calibration and be far more reliable than just calibrating to one.. The Essentials PH meter is a professional and very reliable hand held meter that is used for testing the PH level in a liquid solution. The Essentials PH meter gives you a reading in 0.1 increments, which provides you with a highly accurate reading to ensure you have your solution at the correct level. This PH meter is very easy to use. First turn on the meter and immerse the sensor into your solution and the unit will instantly display the PH reading on the large screen, for you to easily read it. To ensure you are receiving accurate readings time after time, we recommend you regularly calibrate your PH meter with a Buffer solution of a fixed and known PH. Essentials pH meter is designed to give highly accurate readings in 20 seconds! Convenient & easy to use, it is automatically temperature compensated and has 1-3 year life span. This robust meter has built in energy saving mode & low battery indicator.