Psi Index (Traveller)
0 – No training possible, no techniques to control usage (12+)
1 – No training possible, crude techniques to control usage (11+)
2 – Training up to Talent 0, Control 10+. Discovery of natural enhancers
3 – Training to Talent 1, Control 9+. Refinement of natural enhancers
4 – Talent 2, Control 8+. First artificial enhancers.
5 – Talent 3. Second generation artificial enhancers. First artificially induced instances of psionics (unreliable)
6 – Talent 4, Control 7+. First artificial power multipliers, reliable inducement of psionics in a small segment of population.
7 – Control 6+. Stable power multipliers, large scale inducement of psionic powers.

Additional Rules for Psionics:
“Shadow” PSI Points: pool of PSI points under Referee control, equal to PC PSI. Referee may spend these points to activate powers, representing subconscious impulses or external factors that impede control of powers (Subconscious teleport to safety, overwhelming mass of unshielded minds, etc). If these points go below PC PSI, they refresh at the same rate and time. These points may be blocked by the Control skill, with a target shown on the table above. If successful, those points are spent with no effects.
Usage of PC PSI that drops their total below the pool of Referee points triggers a Control roll as the excess power may cause effects in local environment or trigger another power (Referee's choice). Those points are spent until equal to PC PSI.
Control Skill: Used to control psionic powers. Target numbers are by the training available to the Psion,  as shown in the PSI INDEX table (Commonly PI 4 or 5, but may be less). Unlike Talents, skill levels in Control are not capped at the same level as Talents.
If playing in an edition where stats provide a bonus or penalty to rolls, PSI provides the inverse of its current bonus or penalty to Control rolls (Thus, weaker Psions have an easier time controlling their powers). For training purposes, Control maybe self-taught up to any level allowed by your game. During character generation, if you are in the Psion career, gain Control 0 during  basic training and roll 9+ every term (no Dms) to gain one level, up to the normal maximum allowed during character generation.