orfy said:
You've lost me.
If it's a design exercise then fine but if you're thinking of doing it then I really am at a loss as to what is wrong with this method?
Picture this: You have a one-foot tall scale hanging from your ceiling, connected to a balancing beam. Instead of telling you how many pounds are on the scale, it's marked off in ABV- 0%....1%....2%....3%....4%....5%....6%....7%....8%....9%....10%....11%....12%
You set the carboy on the balancing beam, add the necessary amount of counterweight and fidget it around until you've got the scale zeroed out. You then look at the little red indicator on the scale and it says this:
0%....1%....2%....3%....4%....5%....6%....7%....8%....9%....10%....11%....12%
^
Every few days or few hours, or whenever the mood strikes, you walk over and look at the scale. Maybe after a few hours, you walk over and look again and it says:
0%....1%....2%....3%....4%....5%....6%....7%....8%....9%....10%....11%....12%
........^
Then a little later, you check it out:
0%....1%....2%....3%....4%....5%....6%....7%....8%....9%....10%....11%....12%
............................^
Then after a few days you look and you've got:
0%....1%....2%....3%....4%....5%....6%....7%....8%....9%....10%....11%....12%
........................................................^
So you uncap the carboy, take the S.G. just to confirm your reading before racking off to secodary or whatever.
Is it useful? Marginally so, since you can easily recognize a stuck fermentation without continually opening and closing your fermenter to take a reading. More importantly, for folks who have a dedicated brewing space, it's a very easy way to show people what you are doing and how it works. Explain to a total newb how a hydrometer works and what the numbers mean and their eyes will glass over. Point to a little arrow on a scale that says 6.2%ABV and then they will GET IT instantly.
Is it appropriate for someone like me who will be shuttling carboys and brewkettles around his tiny living space? Not really. But if you've got the dedicated space, and if you pride yourself on showing off what you are doing when brewing beer, then this is a very cool gadget (assuming it works). Necessary? Certainly Not. Cool, Easy to explain, Fun to watch, and likely to reduce the risk of infection in your brews? I would say so.