. The pH Standard Solution is available in three sizes and each pack can be formulated with 250ML of Standard Solution. Choose according to your needs A: 3pcs × PH4.00 B: 3pcs × PH6.86 C: 3pcs × PH9.18 D: 1pcs PH4.00 + 1 pc(s) PH6.86 + 1 pc. PH9.18 Instructions: Cut out the plastic bag, pour the powder into a 250ML volumetric flask, rinse the inner wall of the plastic bag with a little CO2-free distilled water, and dilute to the mark and shake well. The calibration solution can be reused without contamination. The shelf life of the powder is 2 years, and the shelf life after watering is about 12 months. How to use the calibration solution: Wash the electrodes with a pH meter with clean water (2-3 times), then immerse the electrodes in the calibration solution and adjust the pH meter to the same value as in the calibration solution. If you want the instrument to be more accurate, you can use two or three calibration points. The so-called two-point calibration is calibrated with two calibration clamps, and the three-point calibration is calibrated with three calibration calibrations. Generally, start the calibration at 6.86. Then calibrate with 4.00 or 9.18. Note: Please allow 1-3cm error due to manual measurement. Make sure you don't mind before you bid. Due to the difference between different monitors, the picture may not reflect the actual color of the item. Thank you! Package Included: 3 Pcs × PH Calibration Buffer Powder (No Retail Package)