I can’t swear these exact values are correct, but this sheds some like on the dividing lines between TR’s Difficulty Level assignments:
- Achievable = 1.0 to current PL
- Productive = 0.1 to 1.0 higher than current PL
- Stretch = 1.1 to 2.5 higher than current PL
- Breakthrough = 2.6 to 4.5 higher than current PL