pH pen meter calibration solution powder with 7.00pH for calibration of electronic pH meters and for testing pH measurement accuracy of other types of pH-tests. Powder from one bag is mixed with 250ml of deionized or distilled water, after which the solution has 7.00 pH at 25°C. Powder bag contains a pH conversion scale for 10°C - 50°C temperatures for convenient use. Sealed pH powder bags have virtually unlimited storage life.