PS:
do not purchase your jumble-sale jacket with a "center back vent". This is a slit in the MIDDLE of the back, down below the waist. if your jacket has splits, then there must be two of them, along the SIDES of the back of the jacket. Those are called "side vents" You're going to open these up, anyway.

Do not buy a jacket that looks like this!!!!!! NO!



You want this.....



Look here. Find the side vents in the back in the lower picture. THAT is what you want.



By the way, that's a bloody gorgeous jacket in that last link, isn't it?