brand new and high quality. The pH pH standard solution is available in three sizes, and each pack can be formulated with 250ML standard solution. Please choose according to your needs A: 3pcs PH4.00 B: 3pcs PH6.86 C: 3pcs PH9.18 D: 1pc PH4.00 + 1pc PH6.86 + 1pc PH9.18 Instructions: Cut the plastic bag, pour the powder into a 250ML volumetric flask, rinse the inner wall of the plastic bag with a small amount of distilled water without CO2, 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 pH meter electrode with pure water (2-3 times), then immerse the electrode in the calibration solution and adjust the pH of the pH meter to the same value as the calibration solution. If you want the instrument to be more accurate, you can use two or three points to calibrate. The so-called two-point calibration is calibrated with two calibration calipers, and the three-point calibration is calibrated with three calibration calibrants. Generally start calibration from 6.86. Then calibrate with 4.00 or 9.18. Note: Please allow 1-3cm error due to manual measurement. please make sure you do not 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 includes: 3pcs PH Calibration Buffer Powder (No retail package)