Beryllium chip

A beryllium chip was a component of some types of atomic clocks.

The clock designed by Professor Wagg used a beryllium chip. The Eighth Doctor stole the chip to repair a malfunction in the TARDIS which had been caused by. (TV: Doctor Who) Daniel Joyce gave Wagg a new beryllium chip. (PROSE: Unnatural History)

The timecode on the holo-prints of Lexy's body was made with a beryllium chip. (AUDIO: Square One)

When the Doctor arrives in a hotel on Earth, 500,002, the receptionist says the clocks can't be wrong, because they have beryllium chips. (AUDIO: The Girl Who Never Was)