A complication (or function) added to mechanical watches to help measure short intervals of time, the chronograph has in the last 200 years measured everything from the duration of horse races, helped calibrate artillery fire, time hot laps around a race circuit, the crew of the Apollo 13 mission even used a chronograph to time a 14-second maneuver that proved critical in their return to earth.

Synonymous with steel sports watches now, the superstars of the horological world – Rolex Daytona, Omega Speedmaster, Heuer Carrera – are all chronograph watches. Though used by enthusiasts now to time more mission-critical operations like how long burger patties stay on the grill, there’s no denying the appeal of a well-made chronograph. Here are a couple of things you need to remember before you buy one.

1. Integrated vs Modular

There are two routes you can take if you go down the path of the mechanical chronograph – the more scenic “integrated” or the more economical “modular”. An integrated movement is built ground-up as a mechanical chronograph movement. The traditional integrated movement has a column wheel and horizontal clutch construction.

This is as good as it gets - the business end of the Datograph

A purist’s delight, these are more expensive to produce but have a more aesthetically-pleasing construction and are usually hand-finished by skilled artisans, the A. Lange & Söhne Datograph being a prime example. Considered by many as the best modern chronograph, the Datograph isn’t cheap though – prices start at around $90,000. Integrated chronograph movements like the Vajoux 7750 have cam-actuated movements as opposed to a column wheel. A famous example is Caliber 861 that powered the Omega Speedmaster supplied to Apollo 11’s crew during their historic 1969 mission.

Modular movements are cheaper to produce and easier to service since the chronograph module is fitted atop a base movement. It’s mass-produced by movement makers like ETA, Sellita, and specialists like Dubois-Depraz. The ETA A31.L21 (Longines Caliber L.895.5) that powers the beautiful Longines Heritage Classic Chronograph 1946 is a good example of a modular chronograph movement. The chronograph module is built atop a base ETA-2892 movement. A modular chronograph like this costs $3,050.

A modular chronograph is cheaper to produce

Some feel that in all but the finest executions, a modular construction will be less precise. The chronograph seconds hand may jump or stutter when started, the continuous seconds or the minutes hand may jump slightly when the chronograph is activated (even the date disk may move slightly), and the feel of the push-piece is not as smooth and buttery. As noted above, modular designs can also generate more amplitude-reducing drag when the chronograph is engaged. In two recent WatchTime tests, a modular chronograph’s amplitude dropped by 73.5 degrees on average when the chronograph was switched on, while an integrated model’s fell by 19.5 degrees.

2. Horizontal vs Vertical clutch

The column wheel and cam issue orders, but other components further downstream transmit the mainspring’s energy to the stopwatch, and once again, there are competing systems. The traditional system uses horizontal or lateral coupling to transmit energy. When the start button is depressed, a wheel mounted on a moveable bridge or lever slides horizontally to link the fourth wheel, which rotates once per minute, with the chronograph center wheel, which drives the chronograph seconds hand. The intermediate sliding wheel is required because if the fourth wheel meshed directly with the chronograph center wheel, the chronograph wheel (and the seconds hand it activates) would run counterclockwise.

A horizontal clutch or coupling lends for a more aesthetic look

The horizontal meshing system is aesthetically pleasing because it enables the owner to watch the chronograph engaging and disengaging. However, meshing teeth can cause the chronograph seconds hand to jump when it starts, and because the teeth used for chronograph coupling have a different shape, or profile, than teeth used for continuous power transmission, regular or continuous chronograph use can cause the teeth to wear. The extra wheels in this system can also sap the mainspring’s energy, affecting the balance wheel’s amplitude, and so, timekeeping. The other main contender in this arena is known as the vertical clutch. Though not as aesthetically pleasing (because the chronograph engagement takes place largely out of sight), this system offers some advantages. It reduces chronograph drag, the chronograph seconds hand does not jump when started, and the chronograph can run continuously without causing excessive wear.

The Daytona Caliber 4130 has a vertical clutch

In simple terms, in the vertical system, the chronograph is always “in mesh” with the timekeeping wheel train, and a clutch engages and disengages the chronograph. The clutch means smooth starts for the chronograph seconds hand, and the “always in mesh” feature means that starting the chronograph does not generate significant additional drag. The drawbacks include cost, poor aesthetics, and the fact that the vertical clutch can be difficult to service. If you’re a traditionalist who will happily trade a bit of precision for the joy of watching your chronograph in action, the horizontal coupling system is for you. If you’re more concerned with precise starts and stops, or if you like to leave your chronograph running all the time, consider the vertical clutch variety. Caliber 4130 that powers the Rolex Daytona, TAG Heuer’s Heuer 02 movement, Seiko’s Caliber 8R48 all feature vertical clutches.

3. Speed vs Measurements

The most common frequency for modern mechanical movements is 28,800 vph (4 Hz). To calculate how many vibrations that is per second, divide that rate by 3,600, which is the number of seconds in an hour (remember that vph is vibrations per hour). Most modern mechanical chronographs have an escapement with a balance wheel that oscillates at 4 Hz (28,800 vibration per hour, vph). Consequently, the chronograph can time events to the nearest to 1/8th of a second. Similarly, a watch with a frequency of 18,000 vph can time events to the nearest 1/5 of a second. A frequency of 21,600 vph yields accuracy of 1/6 of a second. A watch with a frequency of 36,000 vph can time events to the nearest 1/10 of a second. Zenith’s El Primero, with a frequency of 5 Hz (36,000 vph) was the first automatic chronograph wristwatch to measure up to 1/10th of a second way back in 1969.

Zenith El Primero 9004 has two escapements

Some manufacturers, notably TAG Heuer, produced chronographs with two mainspring barrels, two wheel trains, and two escapements that run at different frequencies. The timekeeping escapement can tick along at a leisurely frequency meant for movements that run for years on end (offering low wear and a long power reserve), while the chronograph escapement can operate at a much faster frequency that allows it to measure hundredths or thousandths of a second and beyond.

That faster speed means the chronograph’s mainspring unwinds quickly, so super-fast chronographs typically cannot time multi-hour events. For example, TAG Heuer’s Mikrograph, which measures to the nearest 1/100-second, can time events only up to 90 minutes in duration. The Defy El Primero unveiled in 2017 can measure up to a hundredth of a second now. Impressive as this may sound, you will be hard-pressed to find anyone who measures time intervals of that level of accuracy with a mechanical watch today. However, if you need a chronograph that can measure specific intervals, such as 1/10s of a second, pay attention to both the movement frequency and the chronograph seconds track on the dial to make sure they meet your needs

4. Flyback vs Split-Seconds

On a normal chronograph, the pusher at the 2 o’ clock position is used to start and stop the chronograph, while the one at 4 o’ clock is used to reset it. On a chronograph with a flyback function, you can use the reset function without the need to first stop the chronograph. It was developed for fighter pilots who did not want waste time by stopping, resetting and starting the chronograph whilst crossing a navigational point.

Two column wheels for split-second function on Patel Caliber CHR-29-535

A split-seconds or rattrapante chronograph allows you to time two time intervals simultaneously. Rattrapante in French means catch up and in this type of chronograph, there are two overlapping seconds hands - one, the rattrapante hand, can be operated by means of a third push-piece, usually located at 8 or 10 o’clock. The extra seconds hand allows the timing of a second event, or splits within a single event, say laps within a race.

The Patek Philippe 5370P

A split-seconds chronograph along with the perpetual calendar, the minute repeater, and the tourbillon is among the quartet of high complications that serves as the standard by which all haute horlogerie brands are measured. This year Patek Philippe introduced the Ref. 5370P in platinum with a Grand Feu enamel dial that costs about $250,000.

A. Lange & Söhne introduced the Triple Split in 2018, the world’s first mechanical split-seconds chronograph that can perform multi-hour comparative time measurements. The watch — whose ability to measure both additive and comparative times up to an astounding 12 hours is achieved by additional rattrapante hands on both the minutes and hours-totalizing subdials — represents the next step up in stopwatch complexity from Lange’s Double Split model, introduced back in 2004.

5. Tachymeter vs Pulsometer vs Telemeter

Most chronographs also have calibrated scales, either etched on the bezel or printed on the dial. Most tachymeter scales start at 400, located at about eight seconds on the dial, and end at 60, at 60 seconds, or 12 o’clock. A simple example of tachymeter use involves determining the speed of a car, where time and distance are known. Start the chronograph when the car passes a mile or kilometer marker, and stop the chronograph when the car passes the next marker.

A tachymeter scale on the Seiko SRQ029 chronograph

Look at where the chronograph seconds hand points on the tachymeter scale, and that number represents the car’s speed. The tachymeter can only measure for one minute, and it is typically graduated to show only a certain range of speeds (for example, between 60 and 400 kilometers per hour). The speeds of runners (too slow) and supersonic jets (too fast) fall outside the tachymeter’s range.

A telemeter scale on the Montblanc 1858 Split-Second Chronograph

A Telemeter lets you calculate distance based on known speed and time. It lets the user determine the distance to an event that can be both seen and heard, for example lightning or artillery fire. The user starts the chronograph upon seeing the flash of light and stops the chronograph when he hears the sound. The approximate distance to the event can then be read off the scale.

Montblanc Heritage Pulsograph with a pulsometer scale

A Pulsometer was a feature of “doctor’s chronographs” in the past and allows the user to measure a person’s pulse rate. The scale is typically explained on the dial. For example, it may read “Gradué pour 30 pulsations” or “Graduated for 5 respirations.” The user starts the chronograph and stops it when the   indicated number of heartbeats or breaths has been counted. The seconds hand will point to the number of beats or breaths per minute on the scale. You can see some great examples of pulsometer watches here.

6. Mechanical vs Mecha-quartz

I’m not going to talk about quartz chronographs here, but there is a middle ground for those who want the feel of a mechanical chronograph but don’t want to shell out too much for that experience. Mecha-quartz movements, made by brands like Seiko, has a quartz base but is fitted with a mechanical chronograph module. Not as popular as they used to be, but brands like Yema and Autodromo make examples that you can get under $500. Most entry-level mechanical chronographs will cost you upwards of $1,500.