Visual Basic Express 2005-overflowexception

I am close to completing my project involving calculating various characteristics of an AC circuit. The project has to be done in Visual Basic 2005 express edition.
The project works for most values but very large ones, with these I get overflow exception was unhandled. If I use the Try....catch method and insert a breakpoint in the catch section I can check the values and they appear within the bounds of the double data type eg 4.5441697049225575E+24

scales = ((quantity \ 80) * 80) + 80
This is the specific line which gets pulled up, both scales and quantity declared as double, quantity has, for example, the (calculated) value specified above.
Scales is declared globally, quantity is declared locally.

If I cannot solve this then I shall have to put limits on the inputs but this is undesirable.

Any advice would be great!

 

try using floating point variables instead of the double type. or maybe an unsigned double.