PF Statistics

I have been running pftop for several days.  Some of the PKTS counts were non-zero yestarday.  Today they are zero.  The others appear to be reasonable, as in not cleared recently.  Table statistics include the date/time when the numbers were last cleared.  I could not find anything similar for rules.  For example I have a block of anything coming in on the telnet port.  Last night it showed 290 PKTS.  Today it shows zero.  Is there something in pf that periodically clears the statistics?  I couldn't find anything in the documentation that addresses this.  Thanks,


Update:  today it appears that all of the PKTS counts were cleared.

-- Doug