This webpage:
http://boinc.berkeley.edu/credit.php
attempts to explain the "recent average credit" statistic, but it doesn't match what I'm seeing. It says that the credit decreases by a factor of TWO every WEEK.

I've been contributing to SETI/BOINC for 2 days. I was granted 77.14 credits TODAY and none yesterday. Yet my RECENT AVERAGE CREDIT says 7.63. This doesn't make sense to me. Why is my RAC only ONE-TENTH my total credit after only ONE DAY?? Shouldn't it still be FULL value until about one week later?

Ah, I should have searched first.
I see a couple of explanations from "jm7" about a "glitch" in the calculations for very short times during the beginning of the project.
So I'll expect it to get more "reasonable" after a few weeks.
Thanks JM7!