Following a link from there, I get to https://www.federalreserve.gov/monetarypolicy/reserve-mainte... and this says:

> During each reserve maintenance period an institution must satisfy its reserve requirement in the form of vault cash or, if vault cash is insufficient to satisfy the requirement, in the form of a balance maintained with a Federal Reserve Bank. The portion of the reserve requirement not satisfied by vault cash is called the reserve balance requirement.

In any case, I'm still agreeing with you!