I have been scanning eBait for a jacket, but find the commonly used measurements difficult to work with. I have tried measuring my own jackets, but only get more confused. Any recommendations from those who have purchased used jackets successfully?

I did win one simple Lovat green tweed kilt jacket, which is a perfect fit in the shoulders, OK in the arms, but possibly short in length - but then, I've never had a kilt jacket before. It seems to me that my other jackets have the bottom button fastening over my belly button, which makes sense, as it would allow one to bend over without disturbing the jacket fit. My green kilt jacket's bottom button fastens 4.5" above the belly button. Is that too high? What do you find on yours?