Calibration solution set pH 4.01 / 7.00pH value: 4. 01 7. 00 per 250ml Precise calibration: Accuracy of pH 0. 015 allows highly accurate calibration Easy recognition: Based on the colors, you can recognize the correct solution at a glance (pH 4: red, pH 7: green) Use immediately: Instead of dissolving powder in distilled water first, you can use this solution immediately Long shelf life, batch certificate available on the Internet