Anyone have much actual experience with using a refractometer during fermentation? Not just with how to run the calculations, but in terms of how accurate it can possibly be? I know there is already an inherent problem since refractometers are made to measure plain sugar solutions, and wort has a lot of other junk in it, which is why calculators like beersmith have a calibration value to compensate - but I don't know whether this value really needs to be accurately reset for every individual batch.
I ask because I have used mine this way a few times (using the beersmith calculator and all) and I heard someone saying that it wasn't accurate to do this. So the other day I got curious and tested it side-by-side against a hydrometer and it was way off. Now, my experiment was very poorly controlled (I didn't record a very accurate OG reading before fermentation, I haven't properly set the calibration value used in beersmith, etc) so I am hoping that when I do a more controlled experiment that it will turn out to be accurate - but that'll have to wait for a future batch. I am just hoping that it is not an unavoidable, inherent inaccuracy in using this method due to the very different ways that hydrometers and refractometers work, and how dissimilar worts for different beer styles can be.
In any case, I'd like to hear some personal experiences with it if anyone has any to share.
