As Jashley eluded to, there's a 'settings' page. You may have to press your Offsets button a couple of times to get there. After you've pressed it a couple of times you should see a page containing the setting (either 1 or 0) for inch/metric. It works on our 18i and 21i controllers. I'm not sure if that's what you're looking for or not and I've never fooled with it myself to see the results.
We have a very old (1984) Fanuc 3T that you have to press a key that says "Param" to get to it.