Scientific notation requires numbers to be written as a decimal (integer plus decimal fraction, if necessary) multiplied by 10 raised to a power exactly equal to a positive or negative multiple of 3. "Multiplied by 10 raised to a power" is often written using capital E. This presumably results from writing out big numbers by grouping digits on threes separated by a comma. Or the use of words like milli, micro, nano, kilo, mega, etc., which are separated by factors of 1000. 400/1000 comes to 0.4, and in scientific notation would need to be rationalised to 400 * 10^-3 or 400E-3.