Skill books in Fallout 2 can be used to increase a character's skill in specific areas of study. Using a book removes it from inventory. Other books are used in quests.
In Fallout 2, the amount of skill points gained is equal to 100, subtract the current skill level, divide by 10, and then rounded down. Thus, the maximum a skill can increased by books is up to 91%.
Reading books takes time: 1+(10-INT) hours per book: 1 hour at INT 10, 2 hours at INT 9, and so on, up to 10 hours per book at INT 1.
Maximizing skill point gain
Passive skills are lowered by 10 (%) when the difficulty is changed from Normal to Hard. SPECIAL stats (Strength, Perception, etc) modify skills with a considerable bonus. The game keeps track of this bonus throughout the game, in real time. Any changes to stats, (e.g. chem effects) during the game add to or subtract from this modifier. It is thus possible to reduce any combination of stats to zero, significantly lowering skill values.
It is possible to raise Small Guns, First Aid and Science to 127%, Repair to 118% and Outdoorsman to 115%, in the case of a player whose Perception, Intelligence and Agility are at 10 (possibly more if the player's stats are lower), Endurance is above three, with the listed skills at 91%. To lose Agility and/or Endurance, use Buffout or Monument Chunks, then wait. To lose intelligence, use Mentats and wait, or Psycho. To lose Perception, drink beer, booze, rotgut, etc. If books are used from inventory (by left clicking and dragging) rather than from a weapon slot, any amount of books can be read while under the influence. Time still passes, as can be seen by the day/night cycle playing out, but drug-altered stats will not change, nor will anything of consequence happen in the game, until after the inventory is closed.