Okay... this is good to know on SG. It should be always displayed as a value at room temp... i think the issue is that preboil SG is not actually room temp, but boiling temp. It's doesn't appear to be corrected at all... and the preboil volume is used based on 4% expansion. Then this is compounded by trub losses.
Go back and read what I wrote on my first response to you and I clearly state how the calculation for the pre-boil gravity is made.
The statement that "the program will calculate a larger amount of sugar lost at this step and back calculate to extract more sugar from the grist" i believe is the main issue here. I'm sure there's a way to fix it... Adjusting the trub loss does not logically make me think that my mash eff is going up. i didn't not change crush, or anything related to mash eff. I'd much rather see BH eff and OG go down... because total volume is going up with the same ingredients. This I can deal with though; now that you said this I checked and noticed the mash eff % is going up when trub loss is added. I can go to "design", edit the Bh eff number, go to "session" check mash eff number, toggle back and forth until mash eff goes back to normal. Then I can edit the equip profile and fix the Bh eff number (because none of these are on the same page). It would be nice to have a more graceful way to edit this, but i'm only editing this when i mess with my equipment every few months.
The "easy" way to do this is to take your post boil volume with and without the additional trub loss and recalculate your BHE based upon that ratio. So if you have 10 liters of wort and 1 liter of trub with a BHE of 80% and you increase the trub loss to 3 liters, then the new BHE to maintain about the same mash efficiency would be 80% * (10 + 1) / (10 + 3) = 67.7% It is a pretty straight forward calculation which will get you close enough for starters.
Back to preboil SG... i still can't get this to line up. I could def relate to innacuracies with volumes when measuring ... 1 quart isn't much to be off. However; the SG is a bigger deal... i'm using this value to see if i'm going to hit OG and deciding what todo about it. Things you can do during the boil (boil harder, add DME), and then there are things you can do after (liquor up). But you can't just throw some more DME in after the boil, and you can't boil harder after you've added additions. The error is larger than 4%, there appears to be more going on or trub losses are "helping". I think BS is using the full 4% expansion volume to figure out SG. If so, it seems like we could just reduce it by 4% to give the proper preboil SG to the user.
With my setting the thermal expansion to 2.2%, I end up right on with volume and within a point on gravity. Once you get a feeling for your process, you pretty much know if you are on target or not.
To reproduce this error create a simple recipe with 10lbs malt and 5gallon batch size. Equipment was a "new profile" with nothing changed. Don't change anything but the trub loss... change from 3 gallons to 0 gallons. When it's at 3 gallons we add 3 gallons of water pre-boil to account for the ending 3 gallon loss. I did the math both ways, based on "cooled" preboil volume vs actual pre-boil volume to see if one was correc vs the other. Then i took the OG and multiplied by total volume to get points... divided by "cooled" preboil volume to see what the real target preboil SG would be.
0 gallons trub loss
preboil SG 1.046
est mash eff shows 72%
post boil 5.21g
ending kettle volume 5g (not shown)
batch volume 5g
5.5g pre-boil cooled volume * 46 = 253 points, divide by 5 ending volume = 1.0506 (OG is off..., 6% off)
5.71g "hot" pre-boil volume * 46 = 262.66 points, divide by 5 ending volume = 1.05253 (expected OG, as expected)
Actual pre-boil OG should be (53 * 5g / preboil volume cooled) = 1.048
3 gallons trub loss
preboil SG 1.048
est mash eff shows 115%
post boil 8.33g
ending kettle volume 8g (not shown)
batch volume 5g
8.5g pre boil cooled volume * 48 points = 408, divide by ending kettle 8g = 1.051 (OG is low... expected 1.053, 4% error)
8.83g "hot" pre-oil volume * 48 points = 423.84, divide by ending kettle 8g = 1.05298 (this is the expected OG)
Actual pre-boil OG should be (53 * 8g / preboil volume cooled) = 1.049
Suggestions to make this more user friendly:
1) for thermal expansion on preboil SG/volumes calculate based on the last mash temp. If their mash temp is 154 use that, if they have a "mash out" temp at 168 then use that. This will avoid issues with larger recipes (1.050+ gravities) where my OG and preb-oil SG are off. This would help with teh 1-2% error in preboil volume due to 4% being used rather than 2%, adn it would fix the SG/OG issue. If this is too difficult, we could just deduct the 4% thermal expansion added by BS when calculating SG rather than displaying the SG at "212degF".
You do this by setting the thermal expansion coefficient to the value which corresponds to the temperature you usually take the volume measurement. It is completely in the control of the user. The program does not scale based upon the temperature and does not know at what temperature the user is taking the reading. Nor can it, it is a program, not a mind reader.
2) When for adjusting trub losses allow the user the choice to have BH eff go down /w OG/IBU or mash eff up to make up for losses. This will help alleviate the user nightmare of toggling between "design" and "session" after adding trub losses... fixing the BH eff until mash eff ends up matching reality.
See my calculation above. Again, since the program is designed to calculate sugar extraction based upon the BHE it is up to the user to make the changes. While I would prefer to have it work off of mash efficiency, the designer and others are fine the way it is. I accept that and make the adjustments needed as I change parameters in the equipment profile.
3) Allow users to edit mash eff and have this change BH for them. This would go a long way to help users. I have yet to meet any users who know what their BH eff is... and can enter that when creating profiles. Instead, we all know what our Mash eff and losses are... we enter those values. Since we can't enter mash eff, we end up editing BH eff until it shows the correct mash... and the values are not on the same screens.