LT ATM Def

Key LT ATM Def in Fx Vol Spec refers to a choice from the list ATM Def
The entry here is optional and supplies the ATM (At-The-Money) definition that applies on the ATM vol quotes specified in the column #ATM of the table supplied through the key Vol Set, but only if their associated option expiry T satisfies T >= Tˢʷⁱᵗᶜʰ, where the switch time Tˢʷⁱᵗᶜʰ is specified through the keys Switch Tenor and Switch Date
If missing, the default equals the entry in ATM Def