Running totals show what has piled up. Rates of change show how fast it adds...

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

Running totals show what has piled up. Rates of change show how fast it adds up. With parcels, 120 in a day is not the same as 10 per hour. This article explains how units and time windows shape what a chart tells you, in plain terms.