This morning I did 4 consecutive tests and got the following readings: 16.5, 15, 20, 19. Do any of you have a way of making this test more accurate? In my opinion, the size of the scoop and the dissolving rate of the powder have to be the variable that causes my readings to vary somewhat wildly. To my eye, it looks like the "heaping scoop" is the same size on each test, but who knows. I do know my water sample is identical each time and I'm wiping the end of the titration bottle after 5 drops.