Blood vessels

The views through the eyepiece are drawings of stained sections, not photos of real slides. Your measurements are made on these drawings, taking the ×100 view as 1.8 mm (1800 µm) across. Real vessels differ in size, and the way a section is cut changes how a vessel looks, so a real slide gives different numbers. The red blood cells in the ×100 drawings are drawn larger than they would really look, so that you can find them; at ×100 a real red blood cell (about 7 µm) is only a tiny dot.

The blood pushed along the vein and the enlarged capillary are models: no one can push blood along a slide, and a capillary’s wall is too thin to see clearly with a school microscope.