Today marked the first day of our review of The Metric System (also known as Standard International Units). Students were outside in the courtyard practicing the measurement of various things: their partner’s height, the width of a blade of grass, the volume of the entire courtyard, etc.
Of course, as the students quickly found out, different things require different units. You wouldn’t use meters to measure the width of blade of grass any more than you would use inches to measure the depth of the ocean. Part of being a good scientist is being able to choose the best units to use. Obviously this comes with practice; there are no rules about when to use grams vs. milligrams or centimeters vs. meters. Those decisions are made based on experience.