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| Date: | 1800-1900 |
| Origin: | From normal sight being judged on the ability to read letters at a distance of 20 feet |
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twenty-twenty , 20/20 [uncountable]
1M the ability to see things normally, without needing glasses : 
A pilot must have twenty-twenty vision.
twenty-twenty vision
A pilot must have twenty-twenty vision.2 used to say that it is easy to know what you should have done in a situation after it has happened, but you did not know what to do earlier
