After considering the importance of scale, microbiologists measure the field of view for the 40X and 100X objectives of a compound light microscope. With this information, they calculate the size of a paramecium and a corn stem cell. They also calculate the field of view for the high power objective so that they can use it to determine size. Because of the math and cognitive ability required, the instructional activity is geared toward high school biology scholars. A well-written lab sheet is provided.