Regarding Index based Auctions in Sourcing

Dear Fellow Aribains,

We are using Ariba Sourcing Professional as a part on on demand implementation project.

We have already implemented reverse and dutch reverse auctions for our business procurement.

Now we would like to know its functionality and  how to implement 'Index based Auctions using Amount (or) Percentage' from business point of view.

Can any one share their real time experience in conducting Index based Auctions ?

Thanks & Regards,

Dileep.K