Mac: Set different scroll direction for trackpad and mouse

On OS X El Capitan, I liked the default "natural" scrolling behavior when using the trackpad. However, it also inverted the scroll direction when using an external mouse. The scroll direction option can be found under System Preferences > Mouse and System Preferences > Trackpad. Unfortunately, it does not allow you to set an independent value for Mouse v.s. Trackpad. Luckily, there's an utility app called Karabiner to help us.


Solution:
1. Enable System Preference > Mouse Scrolling direction: natural
2. Download and install Karabiner
3. Launch Karabiner through Spotlight
4. Enable Karabiner core settings > Exclude devices > Don't remap Apple's pointing devices
5. Enable Pointing Device > Reverse scrolling direction > Reverse Vertical Scrolling


Ref:
How to separate "mouse" and "trackpad" settings? - Ask Different