API hardness tests give hardness in degrees, count the total drops, including the first one, to where the solution color changes. Each drop is one degree of hardness, and the sample size is 5 ml. API KH test kits seem to work pretty well, although I don't know how accurate they are. But, I have had a lot of trouble with API GH test kits. Mine have tended to never change color, and the initial color is extremely faint.