Call it the Coffin Bay barometer. Melbourne investment banker and self-confessed expert long luncher David Williams has a novel way of gauging inflation and the cost of living – all from the restaurants he haunts.

“Everyone has a couple of bellwethers and for me, it’s the price of oysters and the other one is the Leeuwin Estate chardonnay,” he told AFR Weekend. “I’m an expert on the prices of both, and I’ll use them as a gauge of where prices are going ... it’s also useful for figuring out how badly a restaurant is trying to gouge me.”