Neither is more correct than the other. They just represent different values.

`1e-9`

is `0.000000001`

; the minus sign applies to the exponent.

`-1e9`

is `-1000000000.0`

; the minus sign applies to the number itself.

The `e`

(or `E`

) means “times 10-to-the”, so `1e9`

is “one times ten to the ninth power”, and `1e-9`

means “one times ten to the negative ninth power”. In mathematical scientific notation, this is usually denoted by a superscript: 1 × 10^{-9} or -1 × 10^{9}. Programming languages adopted the `e`

or `E`

notation because it was easier to type and print than a superscript (and still is, for that matter). (I think this may have been introduced by Fortran in the 1950s, but I’m not sure of the exact history.)