See how a running total differs from a rate of change using parcel deliveries...

https://activecalculus.org/author/Running-Totals-Rates-of-Change

See how a running total differs from a rate of change using parcel deliveries and rainfall. The article explains what each number counts, why units matter, and how choosing a time window—an hour, a day, or a week—changes what a chart can tell you.