I have two Macs: my work MacBook Pro (retina, 15-inch, mid-2014) and my personal MacBook Air (13-inch, bought July 2013). Both are running OS X 10.10.3. When I click on the WiFi menu on my Pro, I see "Personal Hotspot":
It's showing my iPhone 6, running iOS 8.3.
But I don't see that on my Air.
How do I enable Personal Hotspot on my Air?