SETI times

SETI@home reports total CPU time since you installed it. Right now I get:
<snip>
Total CPU time: 79290119.436875
<snip>

Now, I've tried to figure out wehat it's counting, and I can't come up with one. I thought that the Windoze time-slice clock ticked at 20ms, but that doesn't jibe with what a simple calculation (take the last two times reported, divide 20, plus 60^2) should get to correspond to the physical time a WU takes.

BTW, SETI also reports the elapsed physical time since you started running SETI at the end of every WU. You can derive the elapsed CPU time (whatever that is) and the elapsed physical time from them.