I can't measure it on a session by session basis. At least for my issues, I don't think those resolve within one session, so looking at that scale doesn't make sense.

I am lucky in that I have written down a lot of my thoughts prior to starting therapy. Which contain lots of my struggles at the time. What helps me is compare then vs. now. There are very clear differences, for example being fine with my T being gone for about 5 weeks now, vs. not being able to handle a friend cancelling a thing.

It does help that I know of some very clear things that are "goals" to work on. Like fear of abandonment, self harm, mood swings. If I think of any of those things and compare them to how it was a few years ago, I definitely see lots of change. I'm also lucky because I've written down most of my sessions, so I can compare about what we talked, how, what I struggled with... there's clear differences there.