- You may be looking for Doomsday Clock.
The Doomsday Chronometer was a clock created by the Clocksmith to determine, and therefore fix, the end of the universe for the benefit of the Doom Coalition.
History
The Clocksmith built the pieces of the Doomsday Chronometer using metal from the core of Syra, the first planet destroyed in the name of the Sonomancer. (AUDIO: The Doomsday Chronometer) The molten metal was deposited in 14th century Prague by the Eleven's TARDIS, which materialised there briefly after escaping Syra's destruction, and was cooled and taken by the Clocksmith with the help of the Solvers.
In the early stages of his work, the Clocksmith learnt that the Chronometer would not be assembled until 2016 and planned accordingly, taking the ticket held by Liv Chenka to access the piece held at Midge's lost property office (AUDIO: The Eighth Piece) and attempting to have the Eighth Doctor executed by Thomas Cromwell. He also began the Revelation Sect, dedicated to find the lost pieces after the Doctor had Lady Risolva and the Solvers hide them across the planet. (AUDIO: The Doomsday Chronometer)
River Song found one piece in a clock in a shop and boosted its artron energy, (AUDIO: The Sonomancer) leading to it being found by the Doctor in 1998 Calcot and being taken to Midge's, (AUDIO: Absent Friends) from which it was removed by the Clocksmith and taken to his special exhibit in the Science Museum. The Clocksmith managed to find all seven pieces, (AUDIO: The Doomsday Chronometer) including one taken from Thomas Cromwell, (AUDIO: The Eighth Piece) and hid one beneath the Vatican so that nobody but he could assemble the Chronometer.
In 2016, Helen Sinclair took the final piece, stolen from the Revelation Sect in the 1960s, to the Science Museum and, once River was forced to hand over a final missing spring, the Chronometer was completed. It caused a localised earthquake which caused a large amount of damage to the museum and transmitted coordinates of the now fixed apocalypse into the Doctor's mind. The Doctor had the Solvers disassemble the clock and protect the pieces so that it could never be rebuilt. (AUDIO: The Doomsday Chronometer)
Padrac and the Sonomancer learnt from the Doomsday Chronometer the sole time that all galaxies, star systems and planets would be in alignment, planning to use the Resonance Engine at this point to destroy all of the universe bar Gallifrey. (AUDIO: Songs of Love)