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40X 25mm Jewelers LED Lamp Foldable Eye Loupe Magnifier Magnifying Glass Otpvs - Walmart.com

I use something like this and a strong light

For me (and your tests may vary) I test 4k at skin level and it should feel more crisp when it cuts arm hair, for 8k it should start to tree top arm hairs and just touching arm hair at skin level it...

For me, if it can cut arm hair very easily at skin level across the whole length of the blade