Updating Graphs

Actually on this topic....

I am using a function f(x) where x is the number calculated. I am plotting a graph with the data produced.
I have cells going up to 500 in case i decided to use a really small increment, however if i try and set the graph to cover these 500 cells it comes back with an error because currently theres nothing in the cells over about 100, is there any way to have a graph that would automatically update if i changed the increment?

Thanks