efficiency smischiency. let me know how it tastes.
that said. probably reasonable job.
exactly...that's the main issue.
As you dial in your methods & procedures by brewing more, you'll get a better idea of what your own brewhouse efficiency is and you'll be able to formulate beers and achieve desired gravities just by eyeballing it. A gravity reading before the boil helps to determine if the boil needs to be slightly longer or shorter (based on the initial volume and your evaporation rate)...it just takes a couple of batches to get a feel for that.
The software solutions can be helpful at times, but I think the mistake a lot of brewers make is to take the data output by the programs (or a printed recipe for that matter) as some kind of definitive goal. Besides, missing target numbers generated by a piece of software (which can only calculate based on educated guesses as to interpreting the data you input) doesn't constitute failure or a lesser brew.
The bottom line is ALWAYS "how does it drink".
A few gravity points are not all that significant anyway, really. Such variations occur in commercial brewery operations of every size, every day,