When the Rifleman's bolt was first hammered into the bedrock on the shoreline of Hong Kong Island in 1866 by swarthy weather-beaten sailors, Sir Richard MacDonnell had just arrived to govern a young colony of 125,000 people.
Six years before, the Qing dynasty had ceded three square miles of the Kowloon peninsula to Britain after Lord Elgin sacked the Summer Palace outside Beijing. In London, Queen Victoria was in her prime.
Today, the copper bolt sits on a desk in the Murray Building office of Chan Hak. Fourteen centimetres long, it is an important historical relic for surveyors.
By tapping it into the bedrock 131 years ago, the sailors of Her Majesty's Surveying Vessel Rifleman began mapping the land and waters of Britain's new territory in 1866. Now Mr Chan, who is head of the Survey and Mapping Office, wants to put the Rifleman's bolt back as close as possible to its original position, near the present-day Lippo Centre in Admiralty.
'It's a part of the history of surveying in Hong Kong, 1866 was the first time that a vessel came to Hong Kong to do a sounding survey,' Mr Chan said.
The Rifleman's bolt establishes a reference surface for all heights and depths in Hong Kong, which surveyors measure against the lowest tide. The lowest water level recorded by the crew of the Rifleman was 1.23 metres below the average sea level, and this became what surveyors call the Principal Datum.