A single source of wizardry decreases raw spell failure by x75%, two sources by x66.6%, and three by x50%. This is a multiplicative factor, applied after calculating spell failure from skills, though failure is modified by a further modifier.
Generally, the actual decrease to failure rate will be larger than the raw decrease. This is true when your (post-wizardry failure rate) < 50%. For example, wizardry x1 will provide more than a x75% reduction at pre-wizardry failure 66% and lower.
- Big Brain was introduced in 0.27.
- Prior to 0.26, staves of wizardry existed, which gave a rank of wizardry.
- Prior to 0.25, potion of brilliance provided a temporary wizardry bonus.
- Prior to 0.14, a staff of wizardry granted a better wizardry bonus than a ring of wizardry.
- Spell success for details on how wizardry affects failure rate.
- spl-cast.cc:275 (0.25.1)