Changes

There is no hard and fast rule for when to package based on final gravity because the gravity of the finished beer will depend on recipe, process and microbes present among other factors. Generally lower final rgavities gravities are safer because they constrain the extent to which the beer can continue to ferment and generate extra CO2 in the package. But rather than looking for a specific number, pay more attention to the stability of the gravity. If the gravity is stable over a long time scale (weeks to months, depending again on factors such as recipe, process and microbes present), then the beers is probably done. If you are unsure then give the beer a bit longer and monitor final gravity. Each gravity point (.001) of continued fermentation yields roughly 1/2 volume of CO2.