Steps for usage Step 1: Open the package and pour the powder completely into a clean, dry glass container. Step 2: Add 250 ml of deionized water (or distilled water) to the container. (Preferably 250 ml calibration flask) Step 3: Stir until the powder is completely dissolved. Step 4: Calibrate your pH meter, put the pH meter into the solution, stir gently, and wait a few seconds. (Rinse the meter with pure water before testing) To ensure more accuracy, calibrate with 2 solutions, starting from 6.86, then 4.01 or 9.18. Specification: 5*4.01 solution (potassium hydrogen phthalate) 5*6.86 solution (mixed phosphate) 5*9.18 solution (borax) Note: It is not a drinkable solution, please keep it out of the reach of children aged 0-3!