The FRED graph above shows you the total value of checks that are “in the mail.” More precisely, the mail float measures all checks that are being processed—that is, the checks being cleared between banks. The payer’s check is received by the payee’s bank through the mail or handed over to a cashier, but there’s a delay until that check is credited in their bank account. A large fraction of this time is dedicated to the physical delivery of the check through the postal system or other physical means to be processed.

A few more observations about the data. First, there seems to be a very strong seasonal factor until the turn of the millennium. We also see that the mail float keeps increasing over the first four decades, a reflection of a growing economy and inflation. Then it collapses. This shift coincides with the digitization of the check clearing process, which in the end doesn’t require a physical transfer for most checks.

To be honest, we can’t explain the negative numbers in five of the quarters, which implies the payer’s bank subtracted funds before the payee’s bank added them. Time travel may be a factor, but it’s more likely that the method of calculating the mail float—not directly, but as the residual between total assets and total liabilities in checkable deposits—includes some mismeasurements.

How this graph was created: Search for mail float, select the quarterly series for levels, click “Add to Graph.”

Suggested by Christian Zimmermann.