Sure! Thanks for taking a look.
On WCL you can see how much damage was converted to Stagger by placing your mouse over your "damage taken" bar.
Then, looking at your damage taken by ability, you can see how much damage you took from your Stagger dot.
The difference between these two is the amount of Stagger you purified.
I agree that there's no need to try to purify 100% of your Stagger damage, as low stagger isn't going to cause any issues. And this metric is maybe not too useful now because everyone uses Chi Explosion and the purifying happens automatically. Still, I left it in because it's a key part of how the spec works, and newer players may benefit from seeing this number and tracking it across fights.