How to use my own library multiple times

Hi,

for an price calculator i want to create my own library. The calculator gets 2 parameters, an product-object and an rate-object. For multiple products (e.g. in a list) i have to call this lib multiple times. what is the right way in order to use the library or is there a better way for doing that?

Normally i would use
$a = new PriceCalculator(Product1,Rate1);
$b = new PriceCalculator(Product2,Rate1);