Engineering Notation
Engineering notation is a version of scientific notation in which the exponent 
in expressions
of the form 
is chosen to always be divisible
by 3. Numbers of forms such as 
,
, 340, and 
therefore
correspond to engineering notation, while numbers such as 
,
, and 
do
not.
16 of the 20 SI prefixes (excluding centi-, deci-, deka-, and hecto-) correspond to engineering notation.
Engineering notation is sometimes written using "E notation," which represents for example 
as 3.0E9 or 3.0e-9.
Here, the E or e is shorthand for 
and should
not be confused with the base of the natural logarithm 
.
Care must be taken when attempting to infer significant digits from numbers expressed in engineering notation. For example, while 
unambiguously indicates two significant
digits in scientific notation, the number
of significant digits in 
is
not clear, with the only obvious way to indicate significance being to write the
number in the awkward form 
.
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