Brutal

Effects that only work in combat or under a condition are counted as active half the time. The same rule applies to every rune and spell.

Build-dependent ratios such as 10% bonus AD are counted against a reference build (an assumption): 0 / 1 / 2 / 4 finished items at levels 1 / 5 / 10 / 15 (linear in between), each worth the median of the finished items that have that stat (AD 45 / AP 70 / health 350 / armor 40 / magic resist 40). Effects with ratios of two or more types (AD / AP / tank: health, armor, magic resist) count only the highest type (items use their own type), since four finished items can't be four of each type. In the Build Lab's combat power, the ratios use your actual build instead.