does not mean anything.

i would get a three prong tester and test every outlet in every room.

if you are lucky, they check out. This is all you need:

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https://www.amazon.com/Receptacle-Tester-Klein-Tools-RT210/dp/B01AKX8L0M/ref=sr\_1\_2?crid=38FCNSHL5XE9E&keywords=klein+outlet+tester&qid=1663553268&s=instant-video&sprefix=klein+outlet+tester%2Cinstant-video%2C84&sr=1-2-catcorr