At noon on April 6, 1916, the clock tower stationed on top of the Boston Custom House ticked for the first time. One hundred years later, it stands as an iconic landmark for the city, still ticking 24 hours a day.

“It’s quite an honor and a privilege to work on this clock,’’ said David Hochstrasser, who renovated the clock in 1987 and maintains it with his brother.

He said it’s “amazing’’ that the clock still works at all, due to its age and location. The clock endures Boston winters just like the city’s residents, Hochstrasser said, and has survived intense winds, freezing rain, and snow.

“Even on a good day, it struggles to turn those hands out there,’’ said Hochstrasser, who owns a clock shop in Hanover.

He said any minor malfunctions can be “unnerving’’ due to the prominence of the tower.

“When this one doesn’t work there are thousands of people that notice,’’ he said.

The clock sits atop a 500-foot tower above the Custom House, which used to screen goods shipped into Boston. Construction on the State Street building began in 1837, with the tower added in 1915.

Prior to that, customs operations took place at a different location, the waterfront corner of Richmond and Ann streets.

The clock renovations Hochstrasser did almost 30 years ago consisted of replacing the four minute hands on all sides of the tower and restoring some inside pieces, Hochstrasser said. In the 10 years prior to that, the clock hadn’t run at all.

Now, the hands once again are starting to see some wear and tear, he said, and those will soon be replaced.

Ross Hochstrasser, who owns a clock shop in Whitman and assisted with the renovations, also said he is proud to have maintained the landmark for almost a third of its lifetime.

“It’s always been a nice feather in my cap . . . to have the Custom House tower in our portfolio,’’ he said. “I’m always very, very happy to be able to come up here and say, ‘That’s my clock.’’’

J.D. Capelouto can be reached at jd.capelouto@globe.com. Follow him on Twitter @jdcapelouto.