GCDs & Cast Times
Your final cast and recast values depend on your skill or spell speed, your level, and buffs. It is one of the few formulas to include roundup.
GCD1 = ⌊ ( 2000 - f(SPD) ) × Action Delay / 1000 ⌋
GCD2 = ⌊ ( 100 - Type Y ) × ( 100 - Haste ) / 100 ⌋
GCD3 = ( 100 - Type Z ) / 100
GCD4 = ⌊ ⌈ GCD2 × GCD3 ⌉ × GCD1 / 1000 ⌋ × Astral_Umbral / 100 ⌋
GCD = GCD4 / 100
Action Delay must be written in milliseconds. A 2.5 GCD, is equivalent to 2500 milliseconds.
Astral_Umbral is the cast time adjustment Black Mages factor in for Astral Fire and Umbral Ice.