Yocto-

Yocto (symbol y) is a unit prefix in the metric system denoting a factor of 10−24 or 0.000 000  000  000  000  000  000  001.

It was adopted in 1991 by the General Conference on Weights and Measures. It comes from the Latin/Greek octo (οκτώ), meaning "eight", because it is equal to 1000−8. As of 2015, yocto is the smallest official SI prefix.

It can be used to state a subatomic particle's mass, for example:


 * Rest mass of electron:||$0.001 yg$
 * Rest mass of proton:     ||$1.673 yg$
 * Rest mass of neutron:    ||$1.675 yg$
 * Atomic mass unit:    ||$1.661 yg$
 * }
 * Rest mass of neutron:    ||⇭⇭⇭
 * Atomic mass unit:    ||⇭⇭⇭
 * }
 * }