That's the AMASE pod for certain.
To be complete this helicopter is having it's rotor tracked and balanced. The camera to track the blades is mounted on the front part of the left EFAB.
It has to do with wind. When the ball is centered you're flying with no sideslip realtime to the air. In no wind conditions this would result in aerodynamic trim (ball centered) is the same as nose to tail trim (velocity vector straight up). With wind added, a.t. and n.t.t. are not necessarily the same.
When flying NOE, it's advisable to fly n.t.t. since the tail is always right behind the aircraft and you are less prone to whack a tree with it. But with wind you're not flying in aerodynamic trim when flying n.t.t.
Also this applies to all aircraft not just spin wings. It just so happens that the wind vector in slow moving aircraft is more apparent.
Sinclair_76's post in HMCS woes was marked as the answer
If NVG's are installed it would explain why the JHMCS don't work.
Sinclair_76's post in RNLAF Apaches was marked as the answer