Another great range tool feature (Apple)

The range tool trick referenced here? ​

You can also use it to speed/up slow down a clip. Just select the portion you want to go slower or faster - just the specific area you want to adjust inside​ a clip.​

If you choose any value under 30%? I'd suggest changing the View Quality (from the menu category)​ to Optical Flow (an method to create synthetic frames for smoother slow motion.)

FCPX tips like this will be in sessions at NAB/Post Production World