Had to SLAM pool this week bad algae problem. Anyway Last night i do a test before I go to bed to do the overnight test and I get a FC=32.5. Being the clean freak my wife is she accidentally throws the paper out with my reading on it. Instead of going through the trash I figure I will just do a new test. So my next reading is FC=34. Then my curiosity gets the best of me because I wasn't sure the two numbers were the same and I get the paper out of the trash. So now with two different numbers I said what the heck and did another test. Well this one comes in at FC=35. So here is the real question is there a margin of error in these test or am I doing something wrong ( followed directions exactly ).