Imagine you place a slide of a Daphnia under your microscope to view.
You really want to know how long it is but it is so small. You decide to place a ruler with millimeter marks across the diameter of your field of view. You discover your field of view is 2 mm across. Then you remove the ruler and place your Daphnia slide in place. You notice that your Daphnia takes up about one half of your field of view. The Daphnia is therefore