# Telling time

#### TimeClocksMathematicsForces & MotionMeasurementMechanical Systems

For most of us, checking the time is as simple as looking at a watch or a clock—but have you ever wondered how these devices keep time?

The amazing thing about clocks, whether they’re in your home or on the space shuttle, is that they all use the same basic components to tell time:

A power source of some sort A device called a “time base” that keeps accurate time (like the clock’s “heartbeat”) A way to turn that heartbeat into seconds, minutes and hours A way to show the time.

Did you know? In 2009, art experts found what they think is the world’s oldest painting featuring a picture of a watch: a 450-year old portrait, thought to be Cosimo I de Medici, Duke of Florence.

The pendulum clock was one of the first precise timekeeping devices. Here, the weight of the pendulum supplies the power to run the clock. The swing of the pendulum is the clock’s time base and gears are used to convert the pendulum’s swing into seconds, minutes and hours. The face and hands of the clock display the time.

Did you know? In Canada, the time is officially set by the National Research Council of Canada’s cesium atomic clocks.

Wind-up watches were the first popular pocket devices for telling time. A wind-up spring provides the power and a balance wheel that moves back-and-forth (oscillating) inside the watch acts as the time base. Gears inside the watch turn the wheel’s movement into the components of time that are displayed on the face of the watch.

In the 1970s, quartz watches became the most popular way to tell time. Instead of a balance wheel, these watches use pieces of quartz crystal. When an electric charge is applied, the crystals vibrate and create the oscillation that acts as the time base. The electric circuit within the watch converts the oscillation into signals that are sent to an LED or LCD display or to a motor which moves the watch’s hands.

Did you know? The 201-carat Chopard is the most expensive watch in the world. It has three heart-shaped diamonds, a 15-carat pink diamond, a 12-carat blue diamond, an 11-carat white diamond and 163 carats of white and yellow diamonds. The cost? A cool \$25 million.

Digital watches and clocks use the same components as pendulum, wind-up and quartz timepieces, but they do it all electronically instead of mechanically.

More about how watches and clocks tell time

Article first published February 25, 2011.

Photo credit:pnijhuis; stock.xchng

#### Vanessa Caldwell

My job is to write about business, science and technology at MaRS Discovery District, a place in Toronto that helps entrepreneurs turn their research and ideas into businesses. My last job was at a science museum, where I did the following things: wrote the words for animations and exhibits, blew stuff up, played with robots, froze things in liquid nitrogen and, sometimes, dressed in a space suit. When I'm not working, I like experimenting in the kitchen (also known as cooking), knitting, riding my bicycle and daydreaming.