A large cream integral sign with a chip on each part: start day 1 at the bottom hook and stop day 4 at the top hook. To the right, a graph of rate against time: a pink rate line, chip rate, over 3 equal orange strips, one strip per day from tick 1 to tick 4, with teal bands marked dt.

The start day goes at the bottom of the stretched S, the stop day on top, the rate in the middle, and the thin slice of time at the end. Every part has a job.