Floating Point Type
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Floating point numbers are the computer equivalent of scientific
notation. The precise number of significant figures and the range of
possible exponents is machine-specific; Emacs always uses the C data
type `double' to store the value.
The printed representation for floating point numbers requires either
a decimal point (with at least one digit following), an exponent, or
both. For example, `1500.0', `15e2', `15.0e2', `1.5e3', and `.15e4'
are five ways of writing a floating point number whose value is 1500.
They are all equivalent.
Note:Numbers, for more information.