Pool member stats not matching up with local stats

[bitcoinnix]

I'm posting this in newbies so as not to trash up the mining forum with stupid questions -


My worker stats in notroll.in's worker page show 360+ kH/s which is higher than I've ever gotten to with my single 6870, which seems to max out around 290kH/s.

Does anyone know if this is common to be off in pool reporting by a factor of like 70kH/s?