How do money markets work? Specifically Paypal's. 
They say the average yield is 5.04% per 7-day period. Why is it measured in 7-day periods? Flipping through the prospectus it looks like the average yearly return is around 3%. 
I don't get it. 
Do I earn 5.04% once a year? Once a month? 3% once a year? 
Enlighten me 
