from GURPS Magic 2nd edition now called Classic Magic page 15 according to https://forums.sjgames.com/showpost.php?p=2556557&postcount=9
- Extra energy gives a skill bonus as follows: +1 for 20% of extra energy, +2for 40%, +3 for 60%, +4 for 100%, and an additional +1 for each additional 100% of the required energy.
- This method can also be used to make magical items
plus page 19:
- This method can be combined with “energy for skill” (p. 15/B151), to let a mage take a very long time and increase his effective skill.
The 4e rules for Ceremonial Magic removed this, although something like this shows up in GURPS Powers for advantages.