Show interface command

I've noticed something while using this show command
i did this command yesterday, and did it again today
but the values of the counters ( input & output packets , bytes ) was not as i expected
today the values of the counters were less than yesterday
so is these counters counting packets and bytes in a cumulative manner, or what exactly ?

any idea ??
is there any way else to see the traffic history on an interface ??

I did this on a 3825 router, and 2801 router

Regards
                                               
Received on Tue Oct 27 2009 - 10:22:22 ART