Beersmith has a tool to convert your refractometer reading to SG. I have 3 options. The first is unfermented wort, second is fermenting wort, and finished wort.
My question is why the conversion? My SG comes in much lower with the conversion than the unfermented wort conversion. Is it because the alcohol bends the light differently and that needs to be compensated for?
Sorry, first batch with a refractometer (it is an ATC, BTW).
Side note, I don't know if it will help. I am fermenting a light lager. My OG was 9B and now it is 3.9B (1.035 -> 1.004), this is a week into fermentation. Tastes ok, no sour flavors noted, predominant malty sweetness, color pale with good clarity.