I just tested it out to see if it came up with the correct gallon amt. for my tank and it was dead-on. My tank is 42 US gallons and it rec. 37" of fish as stock but said I could go up to some much higher number in the future if I was very careful and experienced.
My bowfront kinda threw it off - I didn't know how to account for the extra water in the bowed part, so for the W #, I just used half way b/n the sides and the deepest part of the bow. It only came up with 35 gals though...