Trending: Watch-watch... Serena Williams' £15 Casio thumps the Fed's Rolex

Serena wears a Casio computer watch, while Federer, right, wears his luxury Rolex (Reuters)

He'd just won his seventh Wimbledon title and Centre Court was going wild, but Roger Federer had been well-drilled by his corporate sponsors, so calmly sat down and strapped on his wrist watch.

In fact, the time from winning championship point to the reassuringly expensive click of Federer's luxury Rolex snapping on was just one minute and 28 seconds. That's fast work from the world's best player – and so it should be for the reported $15m that the Swiss company is paying for him to endorse its timepieces.

It will have been pleased, then, to see his Rolex Oyster Perpetual Day-Date II in prominent place as he held his trophy aloft. But does Rolex really think we'll all dash to Harrods or some other high-end boutique and stump up the £23k for one?

Serena Williams was much more down to earth with her timepiece choice over the weekend. She wore a retro Casio computer watch, which will set you back just £15.95. It's not made of gold and didn't come with a sponsorship deal, but it will help you calculate the odds of Andy Murray making it to the final next year.