The beauty of this 3" diameter (1-7/8" thick) tool is that it's designed for you to lay right on the paper surface and just slide it around to show what you are trying to read. No focusing is necessary. This model instantly caught our attention because the entire lens is glass. This was made for the nautical trade, but even if you don't need the navigator's 360° scale, you'll appreciate its utility. This is just great on any printed surface.