Sorry, wrong Forum ! don't know how to delete.
In the first datasheets (befory july 2005) of the mega 48 etc the initial accuracy of the internal RC osc was stated at +/-1% at 3V 25 degr. The first series of the chips were OK. With a recent batch there was a 7% deviation.
The applications -7 different programs!- didn't work anymore.
In the most recent version of the datasheet the accuarcy is 10%!!
So if you are using the 1% feature of the mega's just like we did you can be just as thankful to atmel as we are