How many?

Micrometres

The micrometre or micrometer, also commonly known as a micron, is an SI derived unit of length equalling 1×10−6 metre; that is, one millionth of a metre (or one thousandth of a millimetre, 0.001 mm, or about 0.000039 inch). The micrometre is often used to measure the thickness or diameter of microscopic objects, such as microorganisms and colloidal particles.

Fathoms

A fathom is a unit of length in the imperial and the U.S. customary systems equal to 72 inches (1,828.8000 mm), used especially for measuring the depth of water. The Atlantic Ocean at its deepest point is believed to be 4,580 fathoms deep.