pH measurements are probably the most common of all routine laboratory tasks. As pH affects all chemical and biochemical reactions, it is very important to have a reliable measurement. pH meters measure the voltage between two electrodes immersed in a sample and compare it to values measured with the same electrode pair in standard solutions. Scharlau standard buffer solutions are accurate, stable and directly traceable to NIST. They are measured performing a multiple-point calibration according to DIN 19268. The calibration standards are prepared according to DIN 19266.