A correction value of +1% when the prism cover is folded up. There are many types of refractometers. A rule of thumb for temperature correction of refractometers with refractive index scales: Subtract 0.0001 to 0.0004 nD per °C with a device temperature of less than 20°, if the temperature … We are going to look at the effects of changing temperature on refractive index measurement and if Temperature Correction can compensate for temperature variances or if actual temperature … Choosing a Refractometer. Refractive index is temperature dependent. Some also include automatic temperature compensation for temperatures between 50-86° F, which eliminates the need to consult temperature correction … Refractometer, Te mperature Correction & Control with a Rudolph J457. Typical temperature coefficients for fluids will be from –0.0001 to –0.0004. Most refractometers measure from 0-32° Brix, with an accuracy of +/- 0.2° Brix. To adjust for temperatures greater than 20oC, please use the following formula: n D 20 = n D T + 0.00045(T - 20 o C) Apparatus This is a view of the front of a refractometer… Once a temperature coefficient is known, the temperature corrected refractive index can be calculated from an actual refractive index reading by the following formula: RITC = ((RT-AT)*TC)+RI Where: RITC = Refractive Index Temperature Corrected The corrected measurement result is therefore -1% + 1% = 0. A slightly more accurate conversion formula is: SG = 1.000019 + [0.003865613(Brix) + 0.00001296425(Brix) + 0.00000005701128(Brix)] Using this formula, a Brix reading of 11 yields a specific gravity of 1.043.