This piece shows how a running total differs from a rate of change, with parcel...

https://atomic-wiki.win/index.php/What_should_I_write_before_doing_any_arithmetic_with_a_real-world_dataset%3F

This piece shows how a running total differs from a rate of change, with parcel counts as a real example. Check units, such as parcels per hour, and time windows, such as one shift or a full week, so you know what piled up and how fast it moved.