Working out which _SDK_ version I'm using

Hi there

I'd like to know, in code, which SDK the app is built with.

I can work out the OS version easily enough, but I need the SDK version - 7.0 or 6.1 at the moment.

Is there a variable set somewhere for that that I'm not finding?

Reason: BTProgressHUD needs to look different in the following situations:

1. iOS6 + any SDK: iOS6 look (no problem, just detect the iOS version)
2. iOS7 + iOS7 SDK: iOS7 look (no problem, just detect the iOS version)
3. iOS7 + iOS6 SDK: iOS6 look (urgh! I can detect iOS7, but not the SDK version, and the app looks like an iOS6 app)

Any ideas? I have a boolean which makes it work, but I want to be able to detect it so the user doesn't have to set that flag.

Ta

Nic