Heath Ledger as the Joker is seen wearing a Casio CA-53W in The Dark Knight.

The digital calculator watch has a plastic case, rubber strap and a keypad that feels like it belongs in a school science lab. It’s unassuming, cheap and oddly fitting for a character who turns Gotham’s hierarchy upside down.

A clever pick for someone who’s always one step ahead — and playing by his own rules.