Understanding vision numbers or readings

The first number is the patient and the second number is the average normal vision.
Patient / Normal
20/20 vision means you can see at 20 feet what a normal person can see at 20 feet.
Even if you don’t start 20 feet from the chart, but say use a handheld chart or one with projectors that you look into like a microscope — used in some drivers license offices — the distance is always adjusted to be equivalent to you starting at 20 feet. So the first number should always be 20 feet. The second number is what tells you if your vision is good or not.

20 / 200 means you can see at 20 feet what a normal person can see at 200 feet. That’s obviously very bad vision.
20 / 50 means you can see standing at 20 feet away what a normal person can see standing 50 feet away.  That’s also not good vision.
20 / 10 means you can see standing 20 feet what a normal person will see standing 10 feet away. That means you have better than average vision.