Could be the coolant temperature sensor playing up. It's hardly a big difference, its not even the thickness of the needle.
Most people probably wouldn't even spot it.
Karls 312bhp A4 3.0 TDI build thread http://www.audi-sport.net/vb/audi-s4...ld-thread.html
Most of the time it's bang on the line but on rare occasions it's like that as pictured. May be a small air bubble?