Any rules of thumb for sizing the Audit Store DB

[dvandeusen]

Hi,  I am just getting into the world of Cognos and was asked to help project the size of different Cognos (8.4.1) components.  I think I have the Content Store nailed and am now looking into the Audit Store.  I am not finding anything in particular so wanted to ask, without giving away any hard-earned secrets, is there a general rule of thumb for projecting the size of the Audit Store?  Logging is set to the most basic level allowed.  I know the number of users and used examples in the Cognos guides to figure out the Content Store and am wondering if given a certain level of logging, whether the Audit Store size can be a projected %'age of the Content Store...to provide a swag of sorts.
Any tips are welcome, thank you, David