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The Hong Kong Observatory's Atomic Clock Serves the Public and E-business
(4 Sep 2003)

You can keep your computer clock accurate if you have access to the Internet.

The Hong Kong Observatory (HKO) uses a Caesium beam atomic clock to maintain the Hong Kong Standard Time, which is the official time of Hong Kong. Members of the public with Internet access can synchronize their computer clocks to the Hong Kong Standard Time using HKO's network time service (Figure 1).

Whenever a request for time check is received from the user's computer, the HKO Internet time server will return a time message based on the Hong Kong Standard Time. The user's computer then uses the received time message and the time delay in receiving the return message to adjust its clock.

Since its introduction in 1999, HKO's network time service has become increasingly popular (Figure 2). In 2002, the number of access to the HKO Internet time server for time checking was over 155 million. During the first eight months of 2003, the average daily number of time checks with the time server exceeded 600,000. This reflects an increasing demand on accurate time which is in line with the growth of e-trade or other e-business where transactions have to be accurately time-stamped. Among those using HKO's network time service are Internet Services Providers (ISP), the Hong Kong Trade Development Council, local tertiary institutions and other corporate users who require accurate time to run their business.

Mr. Ronnie Woo, the General Manager of the Netfront Information Technology Ltd., a local ISP, said "The network time service provided by HKO enables synchronization of our servers to the Hong Kong Standard Time. This protects our operations from the time drift inherent in computer clocks".

Many users of HKO's network time service are individual members of the public who find the service the most convenient way to keep an accurate time.

HKO's network time service is simple to use. Personal computer owners can synchronize their computer clocks to the Hong Kong Standard Time by setting HKO's Internet time server "" as the network time server, either in the operating system (in the case of Windows XP) or in a time client software which can be downloaded free of charge. Details can be found in HKO's website:

Although there are many network time servers around the world, for users in Hong Kong, time check with HKO's Internet time server will provide a more accurate time than time checks with overseas network time servers due to differences in signal transmission time over the Internet. Being the official time-keeper of Hong Kong, HKO also calibrates chronometers for various Government departments to facilitate their law-enforcement operations.

Mr. Chan ying-wa, Scientific Officer of HKO, said, "Every year, HKO helps the Police and the Marine Department to calibrate chronometers that are used for detecting high-speed vehicles on the road and vessels on the sea. Calibrated chronometers are also used to check the duration of dark smoke emission from chimneys by the Environmental Protection Department and in testing construction materials by the Housing Department."

Members of the public who do not have Internet access can check the time by dialing 2926 1133 to the HKO Telephone Information Enquiry System. After choosing the language ("1" for Cantonese, "2" for Putonghua and "3" for English), the caller can get the Hong Kong Standard Time by pressing "4" and then "1". He/She will hear a pip sound and an announcement of the time indicated every 15 seconds. The HKO Telephone Information Enquiry System provided on average 120,000 time checks a year. Members of the public can also check their clocks against the 6-pip time signals of HKO which are broadcast by various radio channels of Radio Television Hong Kong according to pre-set schedules.

Figure 1. Flow Diagram of Hong Kong Observatory's Network Time Service

Figure 2. Hit Rates of Hong Kong Observatory's Network Time Service

Last revision date: <20 Dec 2012>