Dimitris,
You use the vane to stay balanced on the way into and out of the hover, plus into wind when you get there. If you keep the vane pointing noseward you will translate into the wind as you decel. The instruments you saw bouncing are basic flight instruments (from memory Standby ASI top and Standby AoA gauge bottom...but could be well off - time and wine have done their damage). They are being bounced around by the jet efflux from dash two confusing the hell out of the pitots and AoA sensors. They jump as his thrust starts bouncing off the deck.
Edited to add. Or what the chap with the faster keyboard just said!
Last edited by orca; 26th Apr 2013 at 20:59.