Pumping interval

Definition

How often a tank on the book is due, which is what makes the route recur at all.

Why It Matters

A three-year interval on a residential tank means each customer is a third of a job a year, so the size of the book and the size of the year are different numbers. It also decides how quickly neglect shows: a route where intervals have quietly stretched looks steady on last year's revenue and is losing customers who simply have not been called. Ask for the due-date distribution, not the customer count.