For the curious of any age, this 40X Measuring Microscope is an instrument that Isaac Newton surely would have put to good use. With its simple, single focus knob and clearly demarcated metric and imperial measure lines, this is a fun object to play with. Grains of sand look like boulders, and the weave of a flannel shirt like roadways. It has a clear, steady focus, a single eye, and stellar illumination. A simple on-off light switch turns on the illumination light, and the included Allen key easily changes the battery (4 AG9 1.5 V).