Brix Refractometers measure the sugar content of grapes. They cannot measure the sugar content once fermentation has begun due to the presence of alcohol. A hydrometer is used once fermentation has begun.

The following notes apply to all hand held portable refractometers.
1. The hand-held portable refractometer has no electronic components. It does not measure temperature. The compensation is achieved through simple optical elements.
2. It is the temperature of the portable refractometer (which is the ambient temperature) that is important, not the temperature of the sample. In fact, the sample temperature is the refractometer temperature because a drop of sample quickly attains the refractometer temperature.
3. The Portable Hand Held Refractometer is calibrated (nulled) at the mfg. You do not need to adjust it. If you ever need to null it, it is essential that the refractometer with ATC be nulled at 68 F (20 C). [Nulled means setting zero point with a drop of water. This is done by turning the small screw on the top of the unit.] For example, a refractometer with ATCnulled at 77 F will have and error of about 10% at 25 Brix.