Hidden within the service tunnels beneath Sydney's Central Station is a secured room containing a collection of more than 400 heritage clocks and watches.

During their operation they were more than just decorative ornaments; the safe transportation of people and goods depended on their accuracy.

"Timekeeping was really important because you had a baton system where you still needed to make sure there wouldn't be an accident with two trains on the same line at the same time," veteran clock conservator Doug Minty said.

Encased in polished wooden bodies, the clock hands and pendulums might be still but their faces have witnessed the long passing of time, some for well over a century.

Pocket watches were standard issue for employees until they were replaced by wristwatches in the 1970s. ( ABC Radio Sydney: Luke Wong )

Reliable system of timekeeping

Well before the days of smartphones, the railway clock system was one of the most reliable ways for the public to keep accurate time across the distant locations made accessible by trains.

"That was the only means of setting their pocket watch or their clock at home, so they needed the public display of timekeeping by the railways to help them," Mr Minty said.

The heritage timekeeping devices were relocated to the collection room about six years ago following the closure of railway workshops in Strathfield where they were maintained.

Some of the oldest wall clocks, the majority of which were manufactured by American company Seth Thomas, date back to the 1890s.

They were displayed in waiting rooms, refreshment rooms, ticketing and administrative offices.

The refreshment room of Bathurst Railway Station in 1947, complete with a Seth Thomas clock on the far wall. ( Supplied: SRNSW )

By the 1970s there were more than 3,000 mechanical clocks and 6,000 watches working alongside several hundred synchronous clocks, impulse, electrical and mechanical time recorders in the railway system.

An order in the 1980s by then railways chief executive David Hill restricted the selling or gifting of clocks to retiring staff which increased the value of items already on the market.

Some of the clocks had novel modifications and alterations made over the years. ( ABC Radio Sydney: Luke Wong )

"I've seen some for a few hundred [dollars] because they were painted blue and yellow, and others in nice condition can go for several thousand," Mr Minty said.

Today, the majority of railway clocks run on a global positioning system (GPS), many with digital displays detailing the movement of trains for passengers.

Pride in heritage

Protective carry bags, like this one held by Craig McPherson, were used for transporting mechanical wall clocks. ( ABC Radio Sydney: Luke Wong )

Craig McPherson, a heritage specialist at Sydney Trains, said the collection was retained as an important way of interpreting the history of railway stations around New South Wales.

"I think they're quite emotive objects just in themselves and seeing them here en masse you really understand the scale and breadth of how the railways operated across NSW," he said.

Maintenance filing cards were used to record the whereabouts of clocks and their repair histories. ( ABC Radio Sydney: Luke Wong )

At varying times each year the public is invited to view the room as part of the station's behind-the-scenes heritage tours.

Mr McPherson said on occasions some of the heritage clocks had been offered to small museums, while many others remained in use in railway offices.

"There's a lot of pride in having a heritage railway clock in your office."

Doug Minty was regularly contracted to maintain railway clocks around NSW for nearly 30 years. ( ABC Radio Sydney: Luke Wong )

A career like clockwork

During his six decades of working with clocks and watches, Mr Minty has travelled around the country for repair jobs and overseas to speak at horology conferences.

"I've been well rewarded by the museum work I've done and the clocks I've seen and I wouldn't have swapped it for the world," he said.

An example of the master watchmaker's restoration work can be seen daily by commuters passing through Central Station's grand concourse.

One of the few remaining original platform clocks still in operation at Central Station. ( ABC Radio Sydney: Luke Wong )

Standing almost two metres tall, the green painted platform clock hangs on the eastern wall of the concourse and requires manual winding by station staff once a week.

Prior to its installation Mr Minty said his wife jokingly suggested the clock case, which sat inoperable for many years on the patio of their home, would make a good casket one day.

"If we couldn't get it going ... she would lay me in it and bury me in a clock," he laughed.

"I didn't disagree with that, I thought that was a very good idea."