Why are these refractometer scales so far off?

I've been using This picture from beersmith.com of a refractometer (Looks like the same refractometer as mine) scale to go back-and-forth between my brew notes (at the computer) when doing ABV calculations. I sometimes record the SG reading during the brew because I'll have the target OG of the recipe in mind and just not thinking in Brix.

Today, I noticed the scale at beersmith and the one in my refractometer (pic below) are not the same! Shouldn't both just be representative of the mathematical equations to convert Brix Wort SG @ 20C?

Other than a crummy QC process at the factory, is there another reason these two scales would be so wildly different (eg: compare at 16 Brix and then again at 29 Brix)?

Topic refractometer specific-gravity homebrew

Category Mac

1
answered at

Simple. The SG scale is wrong. Only use Brix. A refractometer is incapable of measuring SG. It's an approximation, and in this case especially, it's pretty far off.

Instead of using that SG scale, use a conversion tool like this, which is way more accurate when done properly, both for OG and FG:

https://www.brewersfriend.com/refractometer-calculator/

Cheers.

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