asterisk users - Mar 2005 - Rule of thumb rule for x/x => 1/1 billing

Hi List,

I am writing some basic LCR (Least Cost Routing) AGI script for Asterisk 
written in Perl which I intend to GPL when it's finished and properly 
documented.

In order to have a way to compare rates, I'd like to have some 'rule of 
thumb' rule - which will be overridable - and which converts, say, a 
60/15 rate, or a 30/6 rate into an 'approximate average' 1/1 rate so I 
can compare apple with oranges, i.e. 60/60 @ 0.02 USD vs 6/1 @ 0.025 EUR.

Anybody's got any idea of what might reasonably work?

Cheers,
Jean-Michel.