In Snellen notation, what does the bottom number indicate?

In Snellen notation, the bottom number indicates the distance from which a person with normal vision should be able to read the test type. This means that if someone has a Snellen fraction of 20/20, the bottom number (20) tells us that at a distance of 20 feet, a person with normal eyesight can read the letters displayed. When the bottom number is less than 20, it suggests that the individual needs to be closer to the chart to read it, indicating better than average vision. Conversely, if the bottom number is greater than 20, it implies that the individual has poorer vision than what is considered standard for that distance. This system helps in assessing the acuity and clarity of vision relative to standard human vision capabilities.