OK, you’ve sold me as to why I should track my mood (part 1); so just how do I track my mood?
Obviously, the simplest form of mood tracking is just recording depression and mania on a scale, say, of one-to-ten. You could use a “paper” and “pencil” (look it up on Wikipedia).
You might still notice mood trends but that type of mood tracking is not nearly as helpful as it could be. And the more complicated your case, the more you already know, the more subtle your shifts may be and the less you’ll see using simple methods.
There are far more useful, not to mention easier, options.