In those days there were no time signals and the clock had to be set by the stars using a telescope in the tower at the back of the Large Lecture Theatre. It provided the standard for all time keeping operations within the Department, and was kept in a dedicated tiny room on the second floor of the building.
In due course it became obsolete and largely forgotten, but in the 1970s such objects were coming to be appreciated as historical treasures. In 1977 it was restored to good working order by Mr Evans of the School of Jewellery and installed in the entrance hall to the West Building. Many students will remember it being there and admiring it. In 1997 it was moved to become the central feature of the museum set up between the Large and Small Poynting Lecture Theatres.
By 2014 it was showing signs of age (over 100 years!) and would not keep good time. Fortunately the Head of School was able to find funding to have the clock restored by The Clockworks of London, who have special expertise in these rare clocks. It is now back in its place in the museum and when finally adjusted should keep time to something like 0.1 seconds per day, close to its original specification and as good as ordinary non-radio-controlled digital watches. When you have opportunity please come and admire it, and have a look round the other exhibits at the same time.