A generally useful item in the studio and essential when you are sharpening tools.
With a magnifier you can clearly see the shape at the tip of the blade and the bevel. You can see problems like too many angles on the bevel, an off-axis twist on a v-gouge or the tiny chips left by a coarse or medium stone that still need to be polished away.
The Round Magnifying Glass on the left has a lens size of 2.5" (6.3cm) and is a 2.5x magnifier. Because the lens is large, a greater area is in focus. Great for general use.
The Pocket Loupe on the right has two lenses that are 1.25" (3.2cm) across. The power of each lens is 4x so you can use them individually or stack them up to get 8x magnification. The area in focus is small, but this magnifier really gets you up close so you can see the very tiniest details, perfect for checking blade tips while sharpening. Easy to carry around safely since the lenses slip into their own case.