How do I know if I'm getting better?

[Zephanoa]

Technically THE SSS dummies are good enough. You don't need hard numbers, though they are nice. It is assumed that if you can clear x dummy in a certain amount of time then as long as you can maintain that and not die you will win the fight.

[Lastelli]

It is assumed that if you can clear x dummy in a certain amount of time then as long as you can maintain that and not die you will win the fight.

That assumption is wrong though. First of all, it is completely invalid for 6 jobs, namely healers and tanks, since aggro, mitigation and healing are ignored in SSS.
Second, a 3 min dummy session is not representative of anything since damage is highly influenced by crit, direct hit and proc rate in such a small time frame(and you can even summon a chocobo to help you out lol).
Finally, the implicit assumption that players will be able able to replicate whatever they did in SSS in actual high difficulty content is so asinine that it makes the whole system useless.