I'm not reading any further before I reply to this.
I can't figure out why this is a burr under your saddle. I've donated to BrunWater and to EZWater. Not a lot, but as a thank you for having taken the time and effort to make a spreadsheet, and then making it available.
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I'm a scientist by training. One thing good scientists know is that measurements are key to studying anything. And sometimes, they're imperfect. I can't believe anyone would think that these spreadsheets would produce perfect results given the limits in measuring everything from the malt to the amount of water additions.
So I put in 3 milliliters of Lactic Acid. Am I perfect in my use of a pipette to do that? No. Measurement error. How does the spreadsheet account for that? It can't. And you can't hold it, or the authors, responsible for what is beyond their control.
How about the malt? Do I know exactly how it will perform, and what's more, does the spreadsheet know that? No. And no. At best I'm going to get an average of what often happens.
How am I doing measuring the salts I add? Or is the water exactly, perfectly, the volume I think it is? How about the quality of the RO water I'm using?
Yeah. You want perfection out of something that cannot be made perfect.
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You ask if the "my beer is great" crowd is simply engaging in confirmation bias. I don't know.
What I do know is those spreadsheets give me a level of consistency in my brews, and while I may be off a tenth or even two tenths in pH, it's not enough to matter. I don't expect perfection because the inputs aren't perfect.
And as far as confirmation bias: I have one main criterion for measuring the quality of my beer, besides if I like it. I see if those drinking it have more than one. When they do--and they do a lot--that means they like it. I had two people, literally today, ask to buy my beer.
In fact, I have a local entrepreneur where I live who wants me to brew for that establishment and to sell that beer.
You can call it confirmation bias if you want. I call it excellent beer produced in part by my use of water spreadsheets. And I thank the authors for being part of what I'm able to produce.