[Users] Dispatcher module algorithms

I'm trying to understand a little better the docs for the algorithms in the dispatcher module. What exactly does 'hash over call-id', or 'hash over from uri' mean? The emphasis here is on the use of the word 'hash'. For a given call-id or a given from uri, I think I understand that the selected proxy will always be the same. However, is there any way to determine how this will distribute call volume between proxies? Is there some magic formula that is used (ie the hash) to select the proxy? I'd like to know what it is so I could run some numbers through it and try and understand how it would break up call placement to proxies for certain input values. Doug.