This unit looks at the use of spreadsheets to generate a sequence of values for a recurrence relation. The sequence terms will represent the amounts of pollution in a small loch as the weeks pass by. A dot plot is then formed showing the sequence's terms plotted against the week number. This plot will show clearly how the amount of pollution in the loch changes with time. The idea of the unit is to show how dot plots may help students to visualize the idea of a sequence tending to a limit. It also gives them the insight of seeing that a linear recurrence relation does not depend on the initial amount of pollution in the loch.