Atto-

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Atto (symbol a) is a unit prefix in the metric system denoting a factor of 10−18 or 0.000000000000000001.

The unit multiple was adopted at the 12th General Conference on Weights and Measures (CGPM) in Resolution 8.[1] It is derived from the Danish word atten, meaning "eighteen".

Examples of its use:

SI prefixes
Prefix Base 10 Decimal English word Adoption[nb 1]
Name Symbol Short scale Long scale
yotta- Y-  1024 1000000000000000000000000  septillion  quadrillion 1991
zetta- Z-  1021 1000000000000000000000  sextillion  trilliard 1991
exa- E-  1018 1000000000000000000  quintillion  trillion 1975
peta- P-  1015 1000000000000000  quadrillion  billiard 1975
tera- T-  1012 1000000000000  trillion  billion 1960
giga- G-  109 1000000000  billion  milliard 1960
mega- M-  106 1000000  million 1873
kilo- k-  103 1000  thousand 1795
hecto- h-  102 100  hundred 1795
deca- da-  101 10  ten 1795
 100 1  one
deci- d-  10−1 0.1  tenth 1795
centi- c-  10−2 0.01  hundredth 1795
milli- m-  10−3 0.001  thousandth 1795
micro- μ-  10−6 0.000001  millionth 1873
nano- n-  10−9 0.000000001  billionth  milliardth 1960
pico- p-  10−12 0.000000000001  trillionth  billionth 1960
femto- f-  10−15 0.000000000000001  quadrillionth  billiardth 1964
atto- a-  10−18 0.000000000000000001  quintillionth  trillionth 1964
zepto- z-  10−21 0.000000000000000000001  sextillionth  trilliardth 1991
yocto- y-  10−24  0.000000000000000000000001  septillionth  quadrillionth 1991
  1. ^ Prefixes adopted before 1960 already existed before SI. The introduction of the CGS system was in 1873.

References[edit]

  1. ^ International Bureau of Weights and Measures (2006), The International System of Units (SI) (PDF) (8th ed.), ISBN 92-822-2213-6, archived (PDF) from the original on 2017-08-14