How do I set up tap tempo in Logic Pro X?

You have to set up a shortcut key.

You have to set up a shortcut key. I believe the manual says Shift-t. However, at some point apple must have changed key mapping and currently Shift-t is used for "Rename Take or Comp". I used Shift-Option-Command-T. Once you assign the shortcut key you just continually press the key command. So with my assignment I hold Shift-Option-Command while continually pressing T. The first time you use the key command I believe LPX will pop up a dialog box asking you if you want to use tap tempo.

However, tap tempo did not work for me prior to the most recent update. It does appear to be working in LPX 10.1.1.

There does seem to be some limitations though. It will actually change the tempo when set to bar 1. However, it does not appear to change the tempo anywhere else. However, it will play at the tapped tempo when not on bar 1. You will have to view the tempo it starts playing at and manually add a tempo change in the tempo track.

Actually, they partially got it working. But it's still broken. It's not really setting the tempo correctly.

Wow, who is testing this stuff for apple. Guess we are. I've found soooooooo many problems introduced with 10.1.1.

Actually, forget that last comment about apple testing. Maybe I don't understand what Tap Tempo is supposed to do. Maybe it's working correct in 10.1.1. I thought it would set the tempo at the current bar. But Tap Tempo in LPX seems to server a different purpose.