Per an article on the Blumberg Legal Supplies website:

“Lever Arch Binders… are the standard way the A-4 paper-size world files their paper records. In the United States, the usual way to file papers is in manila files… In the past decade or so, however, that’s begun to change. The efficient, attractive, low cost and easy-to-access Lever Arch Binders, conveniently arranged on open shelving, is gaining popularity.”

And that was six years ago. By now, I expect 40% of Earth’s mass must be efficient, attractive, low cost and easy-to-access Lever Arch Binders.

They also say “A 3” Lever Arch binder holds 525 sheets of paper”, so Lottie’s gathered a *lot* of clues.