How often is the interest compounded on the sub and unsub Stafford loans?

I read the examples on this page (http://www.staffordloan.com/stafford-lo ... t-loan.php) and cannot get the same numbers when trying to compute it on my own.

I've read in a couple of places that the interest is computed daily, monthly, and no more than quarterly. (Obviously three different answers.) Daily makes little sense to me while monthly/quarterly don't give me the correct result.

If you could tell me how often it is compounded and, if possible, some quick and dirty formulas with numbers to help me understand how they are arriving at the final result, that would be great.

Thank you so much.