On the Timex Marlin Jet Chronograph TW2Y89800, the chronograph is an analog stopwatch and the tachymeter is a scale for converting elapsed seconds into an average rate over a measured distance. To time an event, return the chronograph to zero, press the start/stop pusher as the event begins, press it again when the event ends, and read the elapsed time. To estimate speed, time a target over a known mile or kilometer, then read the number opposite the chronograph seconds hand on the tachymeter scale. Never press the pushers underwater.
What the Marlin Jet’s two functions do
The exact watch covered here is the Timex Marlin Jet Chronograph, product TW2Y89800. It has a 40 mm stainless-steel case and bracelet, 20 mm lug width, acrylic/Hesalite crystal, date window, meca-quartz movement, tachymeter scale and 50-meter water-resistance rating.
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Its movement combines quartz timekeeping with a mechanical chronograph module. That hybrid construction gives the chronograph seconds hand a smooth sweep while the watch keeps time from a quartz-powered system. Timex describes the chronograph as a stopwatch: the two external pushers start, stop and reset it.
The tachymeter is not a separate speed sensor. It is a printed numerical scale used together with the chronograph. You must know the distance traveled before the scale can produce a meaningful speed estimate. The result is an average rate for that course, not an instantaneous reading.
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Identify the controls before timing
The Marlin Jet has two chronograph pushers in addition to the crown. Because Timex’s 2024 Higher-Function Analog User Guide covers several watch layouts, its diagrams do not establish a unique letter or subdial label for every Marlin Jet. Use the physical arrangement on your TW2Y89800 rather than assuming that a diagram for another Timex applies.
- Start/stop pusher: starts the chronograph and stops it on a second press.
- Reset pusher: returns the chronograph hands to their zero positions after timing has stopped.
- Chronograph seconds hand: the hand you compare with the tachymeter scale for a speed estimate.
- Other chronograph registers: read them according to the markings on your watch; do not infer their function from a different Marlin or another Timex model.
The regular hour, minute and date displays continue to serve normal timekeeping. The stopwatch hands are the ones that move when you operate the chronograph pushers.
Confirm the model and scale before first use
Model identification matters because Marlin chronographs do not necessarily share the same movement or control layout. Look for the TW2Y89800 reference in the product information or on the watch documentation. The official listing describes this Jet as a 40 mm stainless-steel bracelet watch with a meca-quartz chronograph, date window and tachymeter scale. Those details distinguish it from another Marlin that may use different pusher positions or register functions.
Locate the printed tachymeter numbers around the dial or chapter ring and identify which hand is the chronograph seconds hand. The normal timekeeping seconds display is not automatically the hand to use for the scale. If you cannot tell which register is which, follow the markings on your watch rather than a generic illustration. The Timex guide is intentionally multi-model and warns that an individual watch may not include every feature shown.
Use the chronograph as a stopwatch
Prepare the watch
- Keep the watch above water and make sure you can see the dial and scale.
- Check that the chronograph seconds hand is exactly at zero. If it is not, stop the chronograph if necessary and press the reset pusher. If the hand does not return to zero, stop using the timing function until the watch has been checked by an authorized service professional.
- Choose a start signal that you can see or hear clearly and decide which pusher you will use as start/stop.
Measure an elapsed interval
- Press the start/stop pusher when the event begins. The chronograph begins recording elapsed time.
- Press the same pusher a second time when the event ends. The chronograph stops, preserving the measured interval.
- Read the elapsed seconds from the chronograph seconds hand and any additional elapsed-time register provided on your dial.
- Press the reset pusher only after the reading is recorded. The chronograph hands return to zero and the watch is ready for another measurement.
For repeated measurements, reset fully before the next start. Pressing reset while the chronograph is still running is not part of the standard sequence; stop first, then reset.
Use the tachymeter to estimate speed
A tachymeter assumes that the target travels a known distance. The usual procedure uses one mile or one kilometer and a time within the first minute, because the scale is read against seconds from 60 down toward the scale’s higher values.
Standard procedure
- Measure the course. Mark a definite start point and finish point separated by one mile, one kilometer, or another distance you can state accurately.
- Choose the unit. A one-mile course produces a miles-per-hour interpretation; a one-kilometer course produces a kilometers-per-hour interpretation. The manual also identifies knots as a possible tachymeter unit when the distance and desired rate are nautical.
- Zero the chronograph. The chronograph seconds hand must be at zero before the target reaches the start marker.
- Start on the marker. Press the start/stop pusher as the moving object crosses the start point.
- Stop on the marker. Press the same pusher as it crosses the finish point.
- Read the scale. Find the tachymeter number aligned with the chronograph seconds hand. For a one-unit course, that number is the average rate in the matching unit per hour.
- Reset. Press the reset pusher after recording the result.
The timing points matter. Starting early, stopping late or using an estimated course length changes the result, so the tachymeter cannot make an inaccurately measured course precise.
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Choose a distance and keep the units consistent
A one-mile course and a one-kilometer course can produce the same scale number, but they do not produce the same labeled result. If the hand points to 80 after 45 seconds, the interpretation is 80 miles per hour for one mile, or 80 kilometers per hour for one kilometer. The scale does not convert miles to kilometers for you.
The guide also lists nautical miles per hour, or knots, as a possible unit. Use that interpretation only when the measured distance and the intended rate are nautical. Writing the course unit beside your result prevents a common mistake: reporting a kilometer-based measurement as miles per hour.
For a distance that is a known multiple of one unit, multiply the scale reading by that distance multiplier when the elapsed time remains within the method’s first-minute range. Thus a 1.2-mile course producing an 80 reading gives 80 × 1.2, or 96 mph. State both the multiplier and unit in your notes so someone else can reproduce the calculation.
Understand the tachymeter calculation
For a standard one-mile or one-kilometer course, the scale is a shortcut for the relationship between elapsed seconds and an hourly rate. At 45 seconds, the hand points to 80. Therefore:
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|---|---|---|---|
| 1 mile | 45 seconds | 80 | 80 miles per hour |
| 1 kilometer | 45 seconds | 80 | 80 kilometers per hour |
| 1.2 miles | 45 seconds | 80 × 1.2 | 96 miles per hour |
The third example uses the same scale reading over a course 1.2 times longer than one mile. Multiply the reading by the distance multiplier: 80 × 1.2 = 96 mph. The corresponding metric interpretation is 80 km/h for one kilometer in 45 seconds. Do not label a result in miles per hour when the measured course was in kilometers; the distance unit and the rate unit must agree.
Why the scale works
Speed is distance divided by time. A tachymeter rearranges that relationship for an hourly rate and places the result around the dial, so you can read it without doing the conversion each time. The reading is valid only for the distance represented by your course. If the object takes longer than the scale’s first-minute method or the course is not known, use the chronograph as a stopwatch and calculate the rate separately instead of forcing a tachymeter reading.
Make a tachymeter test repeatable
- Use fixed, visible start and finish markers rather than trying to judge distance while the target is moving.
- Have the same observer operate the pusher and use the same visual cue at both ends of the course when possible.
- Zero the chronograph before every run and write down the scale reading immediately after stopping.
- Repeat the run and compare results. A large spread usually points to reaction-time or marker-placement error, not a different tachymeter formula.
Acceleration and braking also matter. A car that accelerates into the course and brakes at the finish can show the same average as a steadier car at a different constant speed. The tachymeter describes the complete measured interval, not the vehicle’s peak or live speed.
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Practical examples
Timing a car over one mile
Set the chronograph to zero and position yourself where both markers are visible. Start as the car crosses the one-mile course’s start line and stop at the finish. If the seconds hand aligns with 60, the average is 60 mph; if it aligns with 80 at 45 seconds, the average is 80 mph. These are course averages, so acceleration, braking and changes in direction affect the result.
Timing a cyclist over one kilometer
Use a measured one-kilometer course. Start and stop at the two markers, then read the scale as kilometers per hour. A reading of 40 means an average of 40 km/h for that kilometer, not a continuous live speed indication.
Using a longer measured distance
If the target covers 1.2 miles in a time that produces an 80 reading, multiply 80 by 1.2 for 96 mph. The same approach applies to another stated multiple of one mile or one kilometer when the elapsed time falls within the method described by Timex. Keep the multiplier and resulting unit explicit in your notes.
What the tachymeter cannot tell you
- It cannot determine speed when you do not know the course distance.
- It does not measure instantaneous speed, acceleration or deceleration.
- It does not improve the accuracy of an imprecise start or finish signal.
- It is not a GPS, radar, odometer or electronic sensor.
- It should not be read as a guaranteed high-precision measurement; the scale is analog and your timing introduces human error.
For a distance or time outside the practical range of the scale, record the chronograph time and use the ordinary speed formula with consistent units. The Marlin Jet remains useful as a stopwatch even when a tachymeter conversion is inappropriate.
Water resistance and operating precautions
Timex rates TW2Y89800 to 50 meters and describes that rating as suitable for light swimming. Timex does not describe it as suitable for snorkeling or poolside diving. Most importantly, do not press either chronograph pusher underwater. Pressing buttons while submerged can compromise the seals and the watch’s water resistance.
- Operate the pushers on dry land or with the watch safely above the waterline.
- Do not treat “50 meters” as a recommended diving depth; it is the model’s stated water-resistance rating, not a permission to press controls underwater.
- After exposure to water, rinse and dry the watch according to Timex care guidance and have the seals checked at service intervals appropriate to its use.
- Protect the acrylic/Hesalite crystal from impacts and abrasive surfaces; scratches can make the tachymeter markings harder to read.
Troubleshoot a timing that looks wrong
The chronograph seconds hand will not start
Press the start/stop pusher once and observe the chronograph hand rather than the regular minute hand. If nothing moves, check that you are operating the chronograph pusher and not the crown. Persistent failure suggests a service issue rather than a tachymeter-reading problem.
The hand does not return to zero
Stop the chronograph, then press reset. Confirm the hand is aligned with the printed zero position. A hand that repeatedly stops short or past zero needs inspection; do not compensate by mentally adding an offset to every speed result.
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The result seems implausible
- Verify that the course is actually one mile, one kilometer or the stated multiple.
- Confirm that start and stop occurred exactly at the markers.
- Check that the distance unit matches the rate unit you report.
- Make sure you read the chronograph seconds hand, not a regular timekeeping hand or another register.
- Repeat the measurement and compare results; a large spread usually indicates timing or course-marking error.
The manual diagram does not match the watch
The Higher-Function Analog User Guide is a multi-model document and warns that a particular watch may not have every feature shown. Use its general start, stop, reset and tachymeter method, but rely on the markings and physical pusher positions of TW2Y89800 for the actual control layout.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.When the chronograph is useful without the tachymeter
You do not need a measured course to use the stopwatch. Timing a cooking interval, a meeting, a lap or any other event requires only a clear start and finish signal. Start, stop, read and reset in the same sequence. If you later learn the distance, you can use the recorded elapsed time in an ordinary speed calculation, even if the time was outside the tachymeter’s first-minute method.
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Quick reference
| Goal | Action | What to read |
|---|---|---|
| Time an event | Zero → start/stop at beginning → start/stop at end | Elapsed time on the chronograph |
| Estimate speed over one mile | Time the target between measured mile markers | Tachymeter number as mph |
| Estimate speed over one kilometer | Time the target between measured kilometer markers | Tachymeter number as km/h |
| Use a 1.2-unit course | Take the scale reading and multiply by 1.2 | Rate in the same distance unit per hour |
| Prepare for another timing | Stop, record, then press reset | Chronograph hands at zero |
Bottom line for Marlin Jet owners
Use the chronograph whenever you need elapsed time: its start/stop pusher controls the measurement and its reset pusher clears it. Use the tachymeter only after establishing a known course distance, and report the average rate in the same unit as that distance. The 45-second example reads 80 on the scale, meaning 80 mph over one mile or 80 km/h over one kilometer; a 1.2-mile course makes that 96 mph. Keep the pushers out of the water, and verify the exact pusher and subdial layout on your TW2Y89800 rather than borrowing labels from another Timex diagram.
Frequently Asked Questions
How do I start, stop and reset the Marlin Jet chronograph?
Return the chronograph hands to zero, press the start/stop pusher to begin, press it again to stop, read the elapsed time, then press the reset pusher. Use the physical pusher positions on your TW2Y89800 because Timex’s general guide covers several layouts.
Do I need a measured distance to use the tachymeter?
Yes. The tachymeter needs a known course distance. Time the target between fixed markers, then read the scale. Without a known distance, use the chronograph as a stopwatch instead.
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If the target takes 45 seconds over one mile, 80 means 80 miles per hour. Over one kilometer in the same 45 seconds, it means 80 kilometers per hour. The distance and rate units must match.
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Can I use a course longer than one mile or one kilometer?
Yes, when the distance is a known multiple and the elapsed time remains within the guide’s first-minute method. Multiply the scale reading by the distance multiplier; 1.2 miles with an 80 reading is 96 mph.
Does the tachymeter show instantaneous speed?
No. It gives an average rate for the entire measured course. It does not show live speed, acceleration or braking.
Can I press the chronograph pushers while swimming?
No. Timex says not to press the buttons underwater because doing so can compromise water resistance. The 50-meter rating is described as suitable for light swimming, not snorkeling or poolside diving.
Why does the Timex manual show controls that do not match my watch?
The Higher-Function Analog User Guide is a multi-model document and warns that not every watch has every feature shown. Follow its general sequence, but use the markings and pusher arrangement on TW2Y89800.
What if the chronograph hand does not return exactly to zero?
Stop the chronograph and press reset once more. If the hand repeatedly stops short or past zero, have the watch inspected rather than mentally correcting every tachymeter result.
The Bottom Line
Zero the chronograph, start and stop it at clear markers, and reset after recording. The tachymeter is an average-speed shortcut for a known distance: 45 seconds gives 80 over one mile or one kilometer, with units kept consistent. Never operate the pushers underwater.
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