Looks to be about a 20% variance from the low to high side (except the one where you add one scoop of DE for a 60 ft^2 filter). I doubt an error of this magnitude is going to have a major effect on filtration efficiency, though I could be wrong. If you are concerned, you can pick up a cheap digital scale and be quite accurate about how much DE you are adding to your system. In my case, I usually just look at the filter back pressure to determine how much DE (or cellulose) to add. At high speed, if I've just cleaned out my filter and washed the grids, I get 10-11 PSI. When the correct amount of DE is added, this will rise to about 15 or 16 PSI (and when it gets to 20 or 21, its time for a backwash or filter breakdown). This seems to work reasonably accurately for both DE and DE substitutes like cellulose powder. Once I get to this back pressure, I stop adding more. My water is crystal clear and the filtration seems to be working well for the last year or so that I've followed this rule. Obviously, you will have to come up with your own measurements for your own system given plumbing differences.