Manual

444 Units and constants
Prefixes The Units menu includes an entry that is not a unit
category, namely, Prefix. Selecting this option displays
a palette of prefixes.
Unit prefixes provide a handy way of entering large or
small numbers. For example, the speed of light is
approximately 300,000 m/s. If you wanted to use that in
a calculation, you could enter it as 300_km/s, with the
prefix k selected from the prefix palette.
Select the prefix you want before selecting the unit.
Unit calculations
A number plus a unit is a measurement. You can perform
calculations with multiple measurements providing that the
units of each measurement are from the same category.
For example, you can add two measurements of length
(even lengths of different units, as illustrated in the
following example). But you cannot add, say, a length
measurement to a volume measurement.
Y: yotta Z: zetta E: exa P: peta T: tera
G: giga M: mega k: kilo h: hecto D: deca
d: deci c: centi m: milli : micro n: nano
p: pico f: femto a: atto z: zepto y: octo