A dict gives lots of words as antonyms to "fixed"
agitated, flexible, indefinite, insecure, loose, movable, moving, soft, undecided, unfixed, unstable, broken, changeable, impermanent, in disrepair, irresolute
I am trying to distinguish some of them:
The number of verb tenses is fixed, which is 12. In contrast, the number of active users on ELL is not fixed.
In this context, which words could be used?