We remember being in elementary school, when a guest speaker scientist came in. He taught us about microns, or micrometers: what you get if you divide a meter into a million parts (or a millimeter into a thousand parts, whatever floats your boat).
Then he asked if anyone had questions, and of course we had one. Is there anything smaller than a micrometer, we asked. The guest looked at the teacher, shook his head (one of THOSE), and proceed to tell us about nanometers (a micron divided into a thousand).
And then, because we just never know when to stop, we asked if there is anything smaller than a nanometer. The poor guest threw up his hands and ran out of the classroom, never to talk to these pesky kids again. We think we remember it correctly.
Well, there is something smaller than a nanometer! Divide it by thousand, and you get a picometer. Divide that by another thousand, and you get a femtometer, or fermi. (Named by Nobel laureate Robert Hofstadter (Jew), after Enrico Fermi (Sadly, Not a Jew). Hofstadter needed to come up with a name for his work on electron scattering in the nucleus.)
Divide by another thousand? Attometer, zeptometer, yoctometer. That's where the metric system ends.
We wonder if that guest speaker knew that...