Brix to Gravity confusion?

[WishboneBrewery]

It seems everything has a slightly different version.
I have software on my Phone that converts and says one thing, BeerEngine says something else, and http://www.fermsoft.com/gravbrix.php says yet another...

Which is right?

Everything I've worked out is near enough but why the differences?

[Andy]

Give us some examples then

[WishboneBrewery]

Brewzor (Android App for HTC Phone) 11.8Brix = 1.046 (Weirdly this came out at 1.042 earlier while I was Brewing!?)
BeerEngine = 1.046
http://www.fermsoft.com/gravbrix.php = 1.048 (to closest shown)

I think my question really is, "What is the real calculation?"

[Dennis King]

http://brew.stderr.net/refractometer.html
I use this one. comes out at 1048

[Graham]

It is because Brix refractometers are calibrated for sucrose, but wort is mostly maltose, and the two sugars have different refractive indices. For a refractometer to give true s.g in wort it should apply a maltose correction factor, which the refractometer calculator does.

Basic Plato to S.G. gives 11.8 = 1.0475;
Corrected to Brix gives 1.046 using a correction factor of 1.04. You can change the correction factor.

[WishboneBrewery]

Thank you I'll stick with BE then.

[crookedeyeboy]

Ive got Beer Alchemy on my iPhone and it give 1047.

[steve_flack]

BeerAlchemy uses a correction factor of 1.04. It then rounds the number for display.