Refractometer use during fermentation

[Bah]

So I'd been unaware of any difference between using a hydrometer or a refractometer to check the gravity during fermentation. I guess until recently I'd either not thought about using the refractometer or just used it alongside the hydrometer. So I've seen on a few websites that once there is alcohol present, that the readings taken with the refractometer need to be corrected by some factor.

I guess what I'm asking is, does this make sense? is there actually a conversion? For example I have a beer that's been in primary about 8 days and the original measurement (by refract) was 18 brix and the current measurement as of this morning is 8.8 brix. I'd been just converting them and thought that I'd went from 1.072 to 1.035 which is not done so I've been worried the last few days. But Beersmith and the other web sources I've been looking at are saying that with correction my current gravity is around 1.010-1.013 which is almost on the low end even for this beer.

Any thought? Am I ok after all?

Thanks,
Brad

[Mylo]

I didn't run the numbers in BeerSmith - but yes, there is definitely a formula that is based on the OG. Morebeer has an excel file that you can use - or you can go by the formula in BeerSmith (ie. choose "fermenting wort", and put your OG in there). Initial readings are "unfermented wort" - which is basially 4 * Brix.

So, your beer is probably close, if not done.


Mylo