Okay I played a game with a friend today. He was playing Echo in the TIE Phantom. Before he declared his decloak, he picked up his face-down dial and looked at it. Although this is a friendly game, is that legal?

Lue.

Yes, although in a tournament you're supposed to let your opponent know "I'm checking my dial"

As long as he didn't put it back on the table faceup, it's only "checking the dial". Once it's on the table faceup, you've got a strong case to say he's revealed his dial and therefore can no longer decloak.

Rulebook, page 6. "A player may look at his own facedown maneuver dials at any time, [...]."

And a good thing that is too. Even when playing with just two ships, I'll forget what I was planning to do a minute before. Was I going there? Then I better Advanced Sensor a focus first. Why did I plan that maneuver? Ah, of course, I was planning to boost beforehand. Occasionally, I'm more surprised by my chosen maneuvers than my opponents are!

As long as he didn't change his move its legal.