I tried yours for a batch or two but it gave me similar numbers as the morebeer spreadsheet. I'll test it again on my latest batch, I haven't bothered to get a refractometer reading from it post fermentation but I have the rest of the numbers already so it will be easy. I'll report back.
Based on glastctbrew's post maybe I'm doing something wrong, I'll check that too.
Ok, here's what I've got. Two carboys with OG 25.5 brix (1.106 according to beersmith, not confirmed with a hydrometer)
Refractometer readings A - 13 and B -12.8 brix.
The different spreadsheets say:
Sean's: A - 1.0194
B - 1.0172
Notes: There are two different equations in column E for calculating OG from the refractometer reading. version 2.1. One row says 1.106, the rest say 1.107. I used 1.107 for these numbers. The numbers reported are from the "new" column.
morebeer: A - 1.019
B - 1.018
Notes: Spreadsheet calculates OG as 1.108
Beersmith: A - 1.019
B - 1.018
Notes: I'm using the default correction factors, used 1.106 as the OG because that is what beersmith calculates from 25.5 brix.
FG readings with my hydrometer (I double checked calibration) 1.025 and 1.024 after adjusted for temperature. None of them come that close, off by about 5 points across the board. This is similar to what I saw before.
It's possible there is some user error when I wrote down the OG since I usually don't write it down right away and I'm sure I didn't check the temperature of the sample (cooled sample, ATC refractometer). Then again this is the same I saw before. I really do want to do some better controlled experiments some time.