Lol major. (Btw, excellent posts again yesterday in that other thread

)
Mr Monkey, it certainly can be confusing! Not sire if you had a listen to the Basic Brewing Podcast that Bob and I did a few weeks back but some of the points made there are relevant here. In fact, in that I talk about not doing pre-boil corrections.
Many home brewers are lead to believe that brews are repeatable whereas they are not. Even commercial breweries have to make adjustments on every single batch. Now...
For a start that 1.047 reading could have been inaccurate as we mentioned above. But let's say it was correct. (Your EAW is within a few percent so it was probably fairly close - see attached file). But let's imagine though that the volume or gravity reading you took was incorrect and that your evaporation on that day was much lower than normal. You would end up with a weak, watery wort which means either adding DME or putting up with a weaker brew. (The latter option in this case is usually preferable IMO).
If you leave your brews alone until end of boil, you can firstly have a double-check on your readings which is a must because once again you can still have difficulty getting inaccurate ambient wort gravity readings as well. Evaporation has passed by and you now know where you stand.
The BIABAcus efficiency default is actually set a little low we hop so that you end up with a stronger wort than predicted. Later as you get more numbers up your sleeve and know your lowest evaporation rate, then you might choose to adjust the default so you get closer to the right 'amount' of beer.
Gotta race now but ask any more questions you have if that makes no sense which it may not!
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