I've had my refractometer for a while now, but it's taking me a while to make the leap from the Specific Gravity scale found on hydrometers, to the Brix scale found on refractometers. There is probably a super-cool refractometer out there somewhere that has both scales, but mine doesn't.
There are a number of web pages that have a chart to convert between the two, but I find the charts annoying. Some are short and easy to read, but not very useful because they don't have anything but whole values. Others include the values for 10ths of a degree, but make it tougher to find what I want because the list is so long.
Right now, I look at the value in Brix scale displayed on my refractometer, and then calculate the Specific Gravity on a phone app, or look it up on a web page. Eventually I'll leave SG behind, but for now the calculation and conversion process is a crutch.The conversion from Brix to SG is not simple math that you can do in your head, but in the interest of science, here it is anyway:
( Brix / ( 258.6 - ( ( Brix / 258.2 ) * 227.1 ) ) + 1 = Specific Gravity
And here's a nifty calculator that will do the work of converting the Brix scale to the Specific Gravity scale so that you (and I) don't have to: