Humans use relative size to judge the size of the moon. This is why the moon seems bigger and closer when it is near the horizon than when it is high in the sky. When the moon is higher in the sky there are no known objects or frame of references to judge the moon's closeness, and thus, appears smaller and farther away. This is called the lunar illusion. For example, a weight scale can be judged reliable if measures for a 25-pound weight do not vary over time or change for subsequent weightings.
Reliability is an important concept in science.
If a test is not reliable, we cannot find the answers to our questions. Imagine placing a 25-pound weight on a scale and getting a different answer every time. In fact, we most likely would question if indeed the scale is measuring weight or something entirely different. Unreliability would prohibit us from reporting our findings simply because they are not reliable. REM sleep is a sleep period during which your brain is very active, and your eyes move in a sharp, back and forth motion as opposed to a slower, more rolling fashion that occurs in other stages of sleep.