PEAK 2983 Scale Lupe (includes mm reticule scale) - 10xThis is the lupe that Jen uses to measure fountain pen tipping size or line width. There is a ruler in the eyepiece that allows you to make very precise measurements of nib widths. Could be used for any application where you want to measure between 0. 1 and 15mm. Focusing ring can be adjusted to get a very clear view. Peak Scale Loupe 10X has precision constructed achromatic lenses (coated 4 elements, 2 groups), a photo printed scale and focusing