20/20 is normal vision

来源: snwflk 于 2009-06-26 09:52:38 [] [旧帖] [给我悄悄话] 本文已被阅读： 0 次 (116 bytes)
20/40 indicates that you should get as close as 20 feet to see what a person with normal vision can see at 40 feet.
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