Oath Gauge
Official Lodestone Job Guide (Always up-to-date)
Oath Gauge is Paladin's Job Gauge.
Oath Gauge
Upon learning the action 
Iron Will (tank stance) at level 10, a symbol will appear on the screen indicating when it is in effect. Iron Will increases enmity gained from using other actions.
Upon learning the trait 
Oath Mastery, the symbol which indicates the use of Iron Will will change to also display the Oath Gauge.
Oath increases by 5 with every auto-attack: Auto-attack for Paladin occurs every 2.24 seconds. Every ability that uses Oath consumes 50 Oath, meaning that each of these abilities can be used once every 22.4 seconds.
Oath can be used on abilities 
Sheltron and its upgraded version 
Holy Sheltron, 
Intervention and 
Cover.
Simple Mode
Iron Will (Active)
The gauge cannot be displayed in simple mode until learning the trait Oath Mastery at level 35.