Its states to get a precise measurement of chlorine to fill up to the 25 mark, then times by 0.2.....Now reading in the How to section, it says you rarely have to do that, and just use the 10 line mark, and times by 0.5 to save on regeant. Now when I do this at the 25 marker, it reads fc 15.8, and when I do it at the 10 marker, its 12.5...Isnt that a big difference? Because when testing, and you want to be in the normal range, wont that give you a false reading by doing the 10 marker line? And poss get below level and risk of algae bloom.....I bought a big bottle of the DPD powder, so im not worried, but just curious how effective to always use the 10 marker rather than the 25..