Racing chronographs make up a very specific, but highly popular niche of watchmaking. In fact, as a testament to their popularity, the most expensive wristwatch ever sold - at a price tag of $17,750,000 - is a racing chronograph. But before we discuss the remarkable story of that particular watch, let's take a look at what goes into what defines this category.
A chronograph is effectively a stopwatch grafted on top of a normal time-telling watch. Able to record elapsed time on demand, a chronograph is very common in the world of watchmaking. They can be found on both mechanical and quartz watches, as well as both analog and digital styles. Almost all analog chronographs display the elapsed time via a series of sub-dials, which are normally located at two or three of the cardinal points around the dial (most commonly 9, 6, and 3 o'clock).
Within the sub-dials, usually one will serve as the regular time-telling function and display the going/running seconds. Another may show the chronograph minutes (either 30 or 60) and the chronograph hours (normally 12), though this latter function may not be present on watches with only two sub-dials.
What sets racing chronographs apart from the rest, including regular and pilot/dive chronographs, is partly functional and partly stylistic. The major functional feature of a racing chronograph is a tachymeter scale that runs around the edge of the dial. This scale can either be internal (printed on the dial or a surrounding rehaut ring), or external (printed or engraved on a fixed bezel).
"Tachymeter" effectively means "speed measuring instrument". On chronographs, they are used for measuring the average speed of an object as it travels over a known distance. It is particularly useful when there are marked starting and finishing points set. For example, to use a tachymeter scale with the chronograph function to tell the speed of a race car, one would simply start the chronograph the moment the car passes the starting post. Then, when it crosses the finish line stop the chronograph and see which number on the scale the seconds hand is pointing at. The scale features a series of numbers in descending order, which indicate the average speed of the race car. Although the numbers themselves are almost spaced evenly around the dial, the increments between these numbers vary greatly (they actually reduce exponentially as time passes until very low speeds below 100kph are reached).
Most racing chronographs, like most watches in general, tend to be round with pushers mounted on the righthand side of the case on either side of the winding crown. However, there are a couple of other case shapes that have been popular for racing chronographs in the past and are currently enjoying something of a renaissance. Bullhead chronographs, for instance, feature the winding crown at 12 o'clock (between the lugs), with the pushers sticking out either side of it like a bull's horns. Popular brands that produce bullhead chronographs are Omega, Bomberg, and Straton. Less common are cushion-shaped racing chronographs, which have a very strong air of the 1970s about them.
While one would assume a high degree of legibility would be essential for a precision timing instrument, modern racing chronographs are more for show than they are for performing actual trackside duties. As such, they are often used as the Formula 1 cars of the watch industry, with watchmakers seeing these bold and brash timepieces as the perfect canvas for material experimentation or co-branding sponsorship opportunities.
Carbon fiber is an incredibly common material to be used in the decoration of racing chronographs thanks to its prevalence in the automotive industry. Some of the best examples of dials decorated in this way can be seen from brands such as Bell & Ross, Chopard, and Omega.