AVR-Chat

On 5/31/07, dlc@frii.com <dlc@frii.com> wrote:
>   That is a brilliant tuning suggestion!  I never thought of that one
> <chuckle>.  Another "gotcha" when using the internal RC oscillators is
> that they are not as stable over temperature as a resonator or crystal.
> As long as you stay pretty close to the 20-25C temperature range they
> are fine, otherwise they can drift (see data sheet for the drift rate).

that's it exactly..

Now if you want to, you can tune the baud rate observing the bit
edges, predicting where they "should be" vs where you see them, but
that's another level of difficulty.
Using a resonator pretty much eliminates any worries over vcc/temp variations.