beer smith formula

I'm not new to brewing. I have a question. Does anyone know the formula that BeerSmith uses to calculate the grain bill? I for the life of me cannot figure it out. I currently do this.  % of desired grain (total points) / by actual grain points / % of effeciency = total wt in #'s .
So, if my desired target abv. is 1.080. and I want to make 12 gallons. then my grain points would = 960. Pale malt has a grain point of 37 and my brew house efficiency s 75%. i plan on using pale malt at 80% of my grain bill. so, my formula would look like this.
                                0.8(960) / 37 / .75 =
                                  768 / 37 /.75 =
                                  20.75 / .75 = 27.65 lbs of pale malt needed for the recipe. BeerSmith doesn't give me this number. I just wanted to know how to configure it to compare my calculations to theirs.
any help would be appreciated.

The way BeerSmith works is that the user sets the batch size and the brew house efficiency in the equipment profile, along with any process losses.  BeerSmith defines the brew house efficiency as the amount of sugars added to the process which make it to the fermenter.  The program then back calculates from the fermenter to the mash tun, taking any losses in the equipment profile and applying the associated gravity points to that loss to determine how much of the sugars get pulled from the mash.  It then uses the amount of sugars in the mash as a whole based upon the recipe that the user inputs by applying the weight of the grain and the associated potential gravity points of that grain.  It does not adjust the grain bill at all in the recipe unless the user adjusts the OG of the recipe or scales the recipe to a different batch size.

In short the program uses the weight of each grain, whereas you are using the contribution percentage of each grain.

 

I understand the theory. I was just looking for a actual formula to do the base calculations. I appreciate the feedback

So the calculation is basic to almost all of the brewing software:

Sum of (grain weight * gravity point potential) * Brew House efficiency = total gravity points into the fermenter.

Total gravity points into fermenter / volume in fermenter = gravity points/unit volume

gravity points/unit volume /1000 +1 = gravity reading

The program does not evaluate each individual grain, but sums the total potential and works from there.