The background of this page (and the Popup Timer window) act as timing lights.
In normal view, this tool checks the server for updates every 15 seconds and calculates the difference between the viewer's clock and the Timer's clock. Display of green, yellow, and red will be synchronized. The message that the timer has stopped the clock may be delayed by up to 15 seconds (in other words, you may see red even if the Timer has already stopped the clock).
This screen displays in 3 views: Normal (speaker view), Self Timer, and Timer (the person showing timing lights to others). In Timer view, the green, yellow, and red colors are broadcast to everyone watching the Normal view (with a delay of about 1 second). Only one person should act as Timer.
If you are listed on the agenda as Timer, the screen will open in Timer mode. Or you can use the dropdown list in the upper right hand corner to claim that role.
How to set this up as a speaker:
Below: Use Reading Mode in PowerPoint to show slides without taking up the whole screen. Size the PowerPoint window so you can still see the timing light.