For Solid or Liquid Soaps: Set of two pH Reference Solution Powders. Use these replacement PH Reference Solution Powders with your pH Digital Meter Pen Kit. Prepare a reference solution with each of these powders, adding distilled water to make a solution of specific pH level to compare and calibrate your pH Meter Pen with just a touch of a button. No screwdriver needed. Suggestion: Use a new, clean Bell canning jar with a clean lid to make and store your solution. Maintain a minimal air gap above the solution to prevent it from reacting excessively with oxygen or carbon dioxide for extended storage.