Automatically rounding numbers?

["Tijnema !" <tijnema@xxxxxxxxx>]

Hi

How can i disable the automatically rounding of numbers, as i work with
large numbers and when i make them small again, it seems that the last
digits are gone.
example:
12345678901234567890
becomes:
1.2345678901234E+19 = 12345678901234000000

Is there a way to disable this??

Thanks in advance,
Tijnema