The clocks use new technology. How does it work?

The recently installed clocks use the existing wireless network, rather than the previous system on the numbered lines, which used the signal network. Bluetooth receivers are installed in stations and on the front and back car of each train, which act “almost like little GPS devices,” Ms. Hakim said. The transportation authority monitors when trains enter and leave the station, and uses that information to display their estimated arrival times at the next station.

How accurate are the clocks?

“So far, our accuracy rate is 97 percent,” Ms. Hakim said.

What stations have the new clocks?

The new clocks have been installed on the R, C and L lines and the shuttle between Grand Central Terminal and Times Square. Other trains that run through the stations with clocks, like the E train, also display their arrival times on the screens.

When will my station have a clock?

Soon, Ms. Hakim said. The transportation authority is able to install these clocks more quickly than the previous clocks on the numbered lines because it is an isolated project, Ms. Hakim said, and the transportation authority is on track to have clocks installed in every station by the end of the year.