A refractometer measures the gravity of unfermented wort and wine must, and is a great device for both the home beer and wine maker. Refractometers differ from hydrometers as only a few drops are required for each sample. To use, simply apply 1-2 drops of your wort/must to the device prism (clear glass on the front), close the daylight plate (plastic cover) and press lightly so the liquid covers the entire surface, then look through the lens while aiming it at a light source.
This refractometer provides gravity readings in both Brix (0-32% +/- 0.2% accuracy) and Specific Gravity (1.000-1.120 +/- 0.003 accuracy). The device also has automatic temperature compensation (ATC) for temperatures ranging between 50-86 F (10-30 C), so no need for correcting the reading based on what temperature your liquid is - it does it for you. The readings will only be accurate before fermentation, as the presence of alcohol will throw off the calculation.
The refractometer comes in a protective carrying case and includes one eye dropper as well as a small flat head screw driver for calibration.