Editing Brix (section)

===Refractive index===
When a refractometer is used, the Brix value can be obtained from the polynomial fit to the ICUMSA table:

:<math>^{\circ}Bx= 11758.74n_D^5 -88885.21n_D^4 + 270177.93n_D^3 - 413145.80n_D^2 + 318417.95n_D -99127.4536</math>,

where <math>n_D</math> is the refractive index measured at the wavelength of the sodium D line (589.3&nbsp;nm) at 20&nbsp;°C. Temperature is important as refractive index changes dramatically with temperature. Many refractometers have built in "Automatic Temperature Compensation" (ATC), which is based on knowledge of the way the refractive index of sucrose changes. For example, the refractive index of a sucrose solution of strength less than 10 °Bx is such that a 1&nbsp;°C change in temperature would cause the Brix reading to shift by about 0.06 °Bx. Beer, conversely, exhibits a change with temperature about three times this much. It is important, therefore, that users of refractometers either make sure the sample and prism of the instrument are both close to 20&nbsp;°C or, if that is difficult to ensure, readings should be taken at 2 temperatures separated by a few degrees, the change per degree noted and the final recorded value referenced to 20&nbsp;°C using the Bx vs. Temp slope information.

As solutes other than sucrose may affect the refractive index and the specific gravity differently, this refractive "Brix" value is not interchangeable with the traditional hydrometer Brix unless corrections are applied. The formal term for such a refractive value is "Refractometric Dry Substance" (RDS). See {{section link||Brix and actual dissolved solids content}} below.