The Shepherd 24-hour Gate Clock
This is one of the earliest electrically driven public clocks and was installed here in 1852. The dial always shows Greenwich Mean Time (GMT).In summer, Britain converts to British Summer Time (BST), which is an hour ahead of GMT, and the clock then appears one hour ’slow’.

Being a 24-hour clock, the hour hand marks noon (XII) at the bottom of the dial and midnight (0) at the top. The time shown is accurate to half of a second,

The Time Ball
The red time ball on top of Flamsteed House is one of the world’s first public time signals. It was installed in 1833 (though the present one dates to 1919) to enable navigators on ships in the Thames to check their marine chronometers.

The time ball drops daily at 13.00 (GMT in winter, BST in summer). It is raised halfway up the mast at 12.55 as a preparatory signal and to the top two minutes before it drops.

The sign is on the fence near the gate of the Royal Observatory in Greenwich, the place where longitude 0 was determined.
This is one of the first electric clocks, which is also unique in being a 24-hour clock (and not 12 as is customary with analog clocks).
The watch was designed by Charles Shepherd, an engineer and the son of a watchmaker.
The watch was taken on the same day (at 12:46 UK time, 11:46 GMT)
Click for a larger image

The "time ball" is a ball that is on a pole and its position on the pole indicates a special time. The one in the observatory "falls" every day at 1300
The ball was taken on the same day Click for a larger image

The sign is one of two signs depicting subjects related to time and measurements Click for a larger image