IEEE754

The mantissa is also called the significand.

For numbers that are both large AND small, i.e. they have a number of digits in the positive component and also a lot of decimal places such as 10000.00003 the small decimal amount is pushed off the end of the mantissa and lost entirely. This is part of the intrinsic inaccuracy of these numbers.

     2^9            
0 10001000 11110100000000000000000