I've just roughed up a spreadsheet on Excel to use during the brewday to adjust gravity one way or another if it's too high/low.
Basically just follow the flow chart entering in the values as necessary.
If the gravity is too low then you can calculate the extract to add or the length of the boil to reach the correct gravity at a smaller volume.
If the gravity is too high then you can calculate a how much to dilute the kettle to before boiling to reach a larger volume at the correct gravity.
Also, the second worksheet in the spreadsheet is used to figure out the L or Gal per hour boil off.
There's probably something out there already that does these calcs but it was interesting making it.
Anyways, I was wondering if some of you guys/gals could check over the calculations to see if they're all OK, I've punched in a few sets of numbers and it seems to be good but it would be awesome if someone else could check it out.
Link to file: http://rapidshare.com/files/104491668/brewday.xlsx.html
Cheers and beers,