Even though, portable PH meters are easy to use, they require calibration at time to time. And this mega value 3-pack calibration kit is time and money saving. These buffer solution powders come in pre-measured packets: Just mix each packet with 250 mL of distilled water, and your calibration solution is ready. Before purchasing, make sure that your meter uses listed solutions for calibration. Feature - Color: As Shown. - Material: Powder. - Size: 5 x 5 x 0.5 cm. -Included one package of 4.01, one of 6.86 and one of 9.18 calibration solution for all pH needs - Fast and easy. No need to measure, just mix individual packs with distilled water. - Accuracy. Calibration powders enable you to test the pH of your pool, aquarium, water, and more quickly with your pH tester / meter. - Long Term Use. Save time and money by mixing powders in a jar of distilled water. This lets you keep them longer and more readily available without needing more packets.