I understand your explaination, but this is not getting met further.
I've posted earlier what my real goal is. Where I need this conversion for.
I find it strange that when we cast a float fValue(250.84f) to a double the result is about 250.8399996. In this case the precision of the float in only 3 digits and not 7 as said by JasonD.
Can you explain this problem?