The TTL flash power level is pre-set for reasonable exposure at the factory. You can, however, reset the power at the desired exposure level, in ±3/4EV by 1/4EV increments. The preset value is memorized as your personal standard after switching the unit off. This unique system for customizing your level settings, called "MY TTL", is a feature exclusive to Nissin. The usual TTL flash level compensation works based on this customized level.