ceiling is a mathematics primitive that rounds reports the closest integer above a given number. In other words, it rounds the number up. For example, ceiling 5.2 would report 6, and ceiling -4.8 would report -4.

In the model example below, each turtle has a my-money variable that increases or decreases a little bit at each tick. We use the ceiling primitive to round up a turtle's my-money variable because we want to present a label under each turtle showing their current money. If we do not round this variable either up or down, its label would show many floating point numbers such as 1.822882372836, which would be visually unpleasant. We also use the ceiling primitive in setting each turtle's ycor parameter so that the turtles move only when the rounded-up version of their my-money variable changes. If they make or lose only a little bit of money, they remain stationary. Lastly, we use the ceiling and its opposite floor for two of our three monitors in the interface.