The standard gravity readings on a hydrometer are denoted by numbers, starting with 1.000, and incrementing by 10, 20, 30, and so on. These numbers represent 1.010, 1.020, 1.030, and so forth.
The point where the liquid level meets the hydrometer scale is your reading. For example, if the brew is at the spot where the arrow is pointing on the hydrometer below, your reading will be 1.040. 