Pinch to Change Font Size
While reading an eBook, you can easily change the font size level using a pinch gesture, pinching in to decrease the font size and pinching out to increase the font size. The font size cycles between "XX-Small" and "XX-Large", with seven levels of size available. The default initial font size is "Medium".
The actual size associated with each font size level can be set through the ePub Reader Settings, where you can also set the font size directly without cycling through the different level.