Variations are determined by Device Template. There is a device template for each kind of Orbiter, and for each orbiter template, there is a device data setting for the variation to use. Orbiter uses this information to render the appropriate UI for the device.
Device Variations should only be used for large scale differences, and should be used very sparingly, because do keep in mind, that if a variation is proposed, everyone should also design for that variation (because it will appear in Designer for everyone else too.)
Variations were originally intended to differentiate aspect ratios or specific hardware differences that were different enough to warrant an aspect ratio, as such we have the following variations:
* Standard Horizontal (3:4) .. for most devices, TV's, tablets, etc..
* Vertical (4:3)... for PDAs, or other devices that we hold vertically
* Symbian (Cell) for cell phones.
* V2 Standard Horizontal (16:9) .. for widescreen TVs running UI2.
I do believe we need ONE more variation for the wide-screened variants of tablets appearing, such as the 770/N800/N810, called Standard Horizontal (16:9)..but other than that, I see little need for changing this table once this has been added, unless somebody comes up with like..a pyramid shaped display or something. ;-)
You'll notice that with the Cisco 7970, there ISN'T a variation for it, why? because it's got a standard aspect ratio (it's basically a 320x200 display), so instead, a Skin with its own main menu and top designobjs was used (SmallUI).