Good review, but "...guaranteed to sustain tuning." ??What is "sustained tuning'?? Some new technology I've not heard of, obviously, but....what is it?

I live maybe 3-4 miles from an Eastwood dealer, he has loads of them in his shop. Instead of playing all his vintage drool-worthy gear, next time I'm in I'll plug in an Airline or two. Sounds like I've been missing out on some fun guitars!