If you want a quick and easy way to take gravity readings during the brewing process, then a refractometer is the tool for the job. Taking hydrometer readings during the brew tends to be a time-consuming process, and by the time you get a reading it may be too late to react. This is because you need to take a large sample and cool it to get an accurate reading. A refractometer allows you take instant gravity readings, with just one drop, at any point during the boil, or even during the run off of the sparge during an all-grain brew. These 'during the process' readings allow you to add more water or boil longer so you can attain exactly the gravity you desire.
Traditional refractometers without ATC are calibrated to work at 68°F. The ATC function allows you to use the refractometer in an ambient temperature range of 50-86°F (10-30°C). Since your sample is just one drop, and will quickly adjust to the temperature of the refractometer, the temperature of the sample is irrelevant. This unit also comes with a manual calibration knob that is secured with a lock nut. To calibrate place one drop of distilled water on the testing platform and adjust to zero if necessary. The LED light is a handy feature that helps illuminate the sample and make the scale easier to read.
Please Note: This tool is used to measure unfermented wort. Once alcohol is present, the use of a correction table is advised.