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It is a magnifying glass. A microscope is also used but is not technically hand-held and the majority of the time has more than one lens.
Magnifying glass
A magnifying glass is a hand-held instrument used to make an item look larger by magnifying its image when viewed through the lens.
Hand lens
Hand lens.
That sounds like a magnifying glass.
magnifying glass
spy glass
You can look online and use them or you can buy them online or in a store
Binocular
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