A(t) is just the function that you choose to use from the world clock site's photo. Pick any quantity that surprises you and call it . Then assuming that the clock is correct, explain in a paragraph how you calculate the change of per second. Then the change of A(t) per day.
For instance, it could be anything, such as temperature, births, abortions, HIV, world population, infectious disease, etc. Just pick one & use the function A(t) to show the per second change per day change.
I'm interested in the number of people dying due to cancer.
When the clock shows a particular time, i.e. 10:07, click on the "Now" ...
Rate of change is discussed.