Martial Mastery is a passive Attack Strength (AS) boost that incentivizes training in multiple weapon types and is an alternative to going for Elemental Targeting (425). This bonus requires training 2x level in a primary weapon skill, and is lost entirely at known 25 spell ranks. These restrictions effectively limit the bonus to squares.
Secondary and Tertiary weapon ranks are the weapons you have the most training in after your primary weapon skill.
AS Bonus = TRUNC((Secondary Weapon Ranks + Tertiary Weapon Ranks) / 8)
This AS Bonus is capped at +50 and is reduced by 5% for every spell known over 5.
Spell Penalty = (AS Bonus * (((Spells Known - 5) * 5)) / 100)
The following skills qualify for primary/secondary/tertiary weapon ranks.