* Micrometer (µm): One thousandth of a millimeter (1 mm = 1000 µm)

* Nanometer (nm): One millionth of a millimeter (1 mm = 1,000,000 nm)

* Picometer (pm): One trillionth of a millimeter (1 mm = 1,000,000,000,000 pm)

* Angstrom (Å): One ten-billionth of a millimeter (1 mm = 10,000,000,000 Å)

Examples of things measured in these units:

* Micrometer: The thickness of a human hair, the size of bacteria

* Nanometer: The diameter of a DNA molecule, the size of a virus

* Picometer: The distance between atoms in a molecule

* Angstrom: The size of an atom

Let me know if you want more information about any of these units!