evidence: Of course, we still haven’t exactly answered the larger accounting question, whether the Postal Service is making or losing money on the Amazon contract. Using short-term incremental accounting — incremental revenue minus incremental costs — the Amazon contract certainly looks profitable. But any enterprise that uses only short-term incremental accounting to price its products would, over the long run, probably find itself out of business. That’s because incremental cost accounting ignores the common costs (or what the Postal Service calls "institutional" costs) that can’t easily be attributed to any one customer or any one line of business — regular first-class "letter" mail, for example, or second-class newspapers and magazines, or third-class catalogues.