That's what I thought. I was just going to do that, use it as a rough estimate, and do a long SLAM to stay on the safe side. I dont know which link you mean, though.Click the link on the test. Basically your testing your FC at dark and again in the morning to see how much you lose over night.
But, now I'm wondering if I should just wait until payday when I can buy the needed test. I know what it is, I just can't remember the letters well enough to type them out. Begins with an "F" has a dash and then a "D" lol