I'm looking for a pair of adjectives which mean, respectively:
As an example usage:
Due to its everyday use, the balance of a current account can be quite fast-changing, but that of a savings account is more likely to be slow-changing.
And as a demonstrative graph: the value denoted by the red lines is more fast-changing, whereas the green value is a lot more slow-changing. The size of the changes is irrelevant - only the frequency is of importance.
The best I've come up with is volatile for the fast-changing part (probably closest to the third definition at dictionary.com), but I can't think of a suitable antonym. To me, stable has more of a connotation of not changing very much when it does change, as opposed to not changing very often.
If the green and red graphs above are frequently and infrequently changing respectively, then the orange, blue and purple graphs are changing continuously (infinitely frequently) - they're all way off to the "frequently" end of the spectrum.