The KH test kit contains the reagent needed to measure KH. It doesn't contain any standard KH solution. You can use the test kit to make your own 4 dKH solution, by starting with distilled water and adding a very tiny amount of baking soda to some of it. Then diluting further until it takes 4 drops of test reagent to make the water in the test tube change color. That is accurate enough for what the drop checker is supposed to do.