How Are Counts Derived?

I have feed PF now for over 30 days with the new client. When I compare some of my PF stats to my FlightAware stats, I see some differences. This bought up the question, how are various counts derived?

My daily aircraft counts are about 200 more on PF and FA. I read some time ago on the FA forum, that they only count an aircraft once in a 24 hour period. My 30 day aircraft count is 86,xxx for PF and 82,xxx for FA. What is PF's logic for daily aircraft counts?

My 30 day positions count is about 1.6 million less on PF than FA. 5,175,xxx for PF and 6,749,xxx for FA.

Both feeds are from the same RPI/dump1090/antenna.