I'm looking for a pair of adjectives which mean, respectively:

 - Fast/Frequently-changing
 - Slow/Rarely-changing

**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.

[![Fast and slow changing graphs][1]][1]

The best I've come up with is _volatile_ for the fast-changing part (probably closest to the third definition at [dictionary.com][2]), 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.

**By contrast:**

[![Continuous graphs][3]][3]

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.


  [1]: https://i.sstatic.net/gfNcu.png
  [2]: http://dictionary.reference.com/browse/volatile
  [3]: https://i.sstatic.net/mQjKT.png