 But the thing about the system was the customer kept the book. Maybe you see the problem with this. All the time, customers would show up at the store and say, I lost my book. And Isidore would say to them, it's okay. What do you think you owe? And then they'd say some not very high number, and he'd write it down and hand them a new book to take home. Years later, my dad became a certified public accountant.