I also question the statement that calculators are only for compounds.
If all the arrows are hitting nock right, that would normally indicate a stiff arrow. If I put the specs in for a 28" 1535, and a Samick Sage that is 45# @ 28", but drawn only 26", then it looks like it would take a 200 gr point to be close. I used a 26" draw in the example because the person who started the post said he used the "clothespin method" and then added an inch. Why add the inch? And most of us do draw a little longer when demonstrating only our draw and not actually shooting, so I poked in 26".
I would bet if we had a really good draw measurement, good center cut information, to include the strike plate thickness and actual draw weight at either the specified 28" or at the actual draw length, Stu's calculator (and I think 3 Rivers calculator was derived from that) would be very, very close.