So when I’m done sparging I take a wort gravity measurement so I know what kind of efficiency I got and where I can expect to be at the end of the boil. If I come in low I need to either boil off more or add some Dried Malt Extract (DME.) If I come in high I need to boil off less or add some water. Of course to figure out the exact details I either need to manually do the calculations or run inside to my laptop and ProMash.
To avoid this hassle I’ve coded up some calculators that I can access from my mobile phone. You are welcome to use them as well and provide feedback on how they work on your phone. Check them out at www.slobrewer.com/mobile.