Advantage in the exchange is REALLY difficult to measure, it depends
strongly on position, and FIDE-CHESS is a notorious example. G.M. Tigran
Petrossian, ex-world champion, was famous by a strict positional Quality
sacrifice in some openings, giving its Rook for a Knight without any
apparent advantage. After a lot of moves, say 20 or 25, the advantage was
notorious, but not easy to see at first!.
