Based on my analysis of pen pressure ranges, I have developed this simple rating scale for IAF and max pressure. This represents my initial thinking and I expect to revise this in the future based on feedback.
For more general information about pen pressure go here: pen pressure
Consider this diagram to be a DRAFT. it will evolve as I learn more.
I think the pressure categories here (EXCELLENT, VERY GOOD, etc) are reasonable.
But be aware, that for a specific pen there can be significant differences for IAF and max pressure for individual units.
Manufacturers
From tablet experts such as Kuuube
And my own measurements: https://1drv.ms/x/s!Aml8i4Jd6crCkTerfXD_1zsIxg3A?e=2aCPfI
Pens, even of the same model, vary in how their pressure handling
Drivers can potentially affect IAF.
Comments on pen pressure levels and ranges for Wacom products: https://www.reddit.com/r/wacom/comments/10l0ujb/comment/j5u1v3z/?utm_source=share&utm_medium=web2x&context=3
Comparison of minimal gram-force ("initial activation force"/"initial activation pressure") recognized by various digital pens and digitizers ( https://www.reddit.com/r/stylus/comments/opc44f/comparison_of_minimal_gramforce_initial/)
Initial Activation Force / Initial Activation Pressure Cintiq Pro 16 2021? (https://www.reddit.com/r/wacom/comments/v9989o/initial_activation_force_initial_activation/)