Keira Knightley wears a Swatch Black Plastic Watch

For most of Everest, Keira Knightley acts with a telephone. She plays Jan, the pregnant wife of expedition leader Rob Hall, and the film keeps leaving the mountain to find her at home in Christchurch, lying awake with the receiver against her ear, taking the calls and counting the hours. Her scenes are the part of the film that never leaves the ground.

The film restages the 1996 disaster, a storm that killed eight climbers high on Everest over two days in May. Rob Hall (Jason Clarke), a New Zealand guide who took paying clients to the summit for a living, is one of them. Stranded above the South Summit and out of oxygen, he reaches Jan one last time through a radio patched to a satellite phone, knowing he will not get down.

The watch she wears belongs to that world below the mountain. Propstore, which later sold the piece with a certificate of authenticity, identifies it as a black Swatch: a plastic quartz on a black silicone strap, with a black dial and white hands, the jewellery she has on at the Christchurch airport as she sees Rob off. It is the cheapest object in a film full of crampons and oxygen masks, and the only one whose single job, keeping time, is the whole of what Jan is left to do. She was pregnant all through the expedition. Their daughter, Sarah, was born after Rob died on the mountain.