The Speedmaster by Omega has been the official chronograph watch for Nasa astronauts since 1965.

The Cosmograph Daytona by Rolex is popular in motor-racing circles.

Today, quartz chronographs have replaced mechanical ones for recording sporting events with the precision of a thousandth of a second, which often can make the difference between gold and silver medals.

Watch experts say most buyers choose chronographs for aesthetics rather than practicality. Wearing a mechanical chronograph has become a fashion statement. Due to the number of subsidiary dials and mechanical complexities involved, chronographs tend to be bigger and thicker in size than other watches. Traditionally, chronographs were worn only by men.

Many brands have also launched chronographs for women in recent years. Breguet launched the marine collection for women in 1998, making the smallest self-winding chronograph movement in the world, with the dial measuring only 30mm in diameter.

The average women's chronograph is 36-38mm in diameter, although they're becoming even bigger. Some women prefer men's or boy's sizes to make a fashion statement. Rolex's boy sizes have been so popular among women that the brand calls its Oyster 31mm 'the man's watch women prefer'.

How it works

Apart from telling the time on the main dial, a chronograph watch usually has a seconds hand, and two or three subsidiary dials with different scales to indicate the elapsed hours, minutes, and seconds. Typically, the three indicators are seconds, 30-minute and 12-hour registers. There's no set location for the subsidiary dials, but most brands tend to keep the layout consistent across their product range. The seconds dial correlates to the time on the main dial, and moves regardless of whether the chronograph function is activated.

A chronograph has two cylindrical push-buttons on the watch case at the two o'clock and four o'clock positions. The stopwatch function is activated when the start-stop button is depressed. When timing begins, the seconds hand starts moving and, after a complete circle or one minute, the 30-minute indicator jumps one position. When 30 minutes has passed, one complete cycle of the 30-minute register is complete, and the 12-hour dial jumps a position. When the start-stop button is depressed again, it stops recording. To reset, you press the button on the four o'clock position.

Other chronograph scales such as fly-back, telemeter or tachymeter are more complicated, and aren't commonly used. The fly-back function (commonly known as the lap-timer function in quartz watches) allows you to record sequential split times. Pushing the reset button when the stopwatch function is running causes the seconds hand to return (or fly-back) to zero, therefore recording another timing sequence, without having to stop and reset. A telemeter measures the duration of a phenomenon, such as the time elapsed between the flash of a lighting and the sound of the thunder, while a tachymeter measures the speed of a moving object over a known distance.

Buying tips

Always buy from an authorised luxury-watch dealer. Ensure the serial numbers on the back of the chronograph are registered with the watch manufacturer. Due to their mechanical complexities, chronographs are generally more expensive than other watches. As with purchasing any watches of value, you should have an understanding and appreciation of the watch's specifications, other than its aesthetic appeal. Decide if you need additional features because more functions usually mean bigger and heavier cases, not to mention heftier price tags. Prices for chronographs vary substantially, depending on the functions, the materials used in the watch, and the brand. Obviously, the likes of precious metals and diamonds will increase the cost substantially. Chronographs that incorporate more functions such as date-day-month indicators and moon-phase displays are more valuable.

Shopping list

IWC

Shop G29, G/F Prince's Building, Central, tel: 2525 5323.

IWC has a wide selection of chronographs inspired by different sports.

Vacheron Constantin

Shop OT287, Level 2, Ocean Terminal, TST, tel: 2735 8481.

The limited-edition platinum chronographs feature telemetric and tachymetric scales.

Hublot

Hublot doesn't have a store, but is available from Dickson Watch and Jewellery, the Landmark, Central, tel: 2521 4245. For other stockists, tel: 2110 4410.

Since its launch last year, Hublot Big Bang chronograph has won several awards, including best design 2005 at the Grand Prix of Geneva. The Big Bang Aspen in white ceramic is designed with women in mind.