Most people glance at a chronograph and see two things: a stopwatch and a busy dial. But the extra scales ringing that dial are actually two of the oldest problem-solving tools in watchmaking — the tachymeter and the telemeter. Both exist for one purpose: to turn elapsed time into something you can actually use, whether that's your speed on the road or the distance to a storm on the horizon.
The Wancher TENJI Chronograph is one of the few watches today that carries both scales on a single 38mm dial — a genuinely rare pairing in modern chronograph design. This guide breaks down exactly how to read each one, so the next time you're wearing TENJI, you know how to put it to work.
What Is a Tachymeter?
A tachymeter is a scale — usually set on the bezel, or on TENJI, as an inner ring close to the dial's edge — that converts elapsed time into speed. It answers one question: if this event took X seconds, how fast is it happening per hour? km/hr
The tachymeter scale gives a direct reading only if you time an event over exactly 1 km (or 1 mile). Start the chronograph at the first marker, stop it at the marker exactly 1 km later — wherever the chronograph hand lands is your speed in km/h.
The tachymeter scale only gives you a direct answer when your distance is exactly 1 km (or 1 mile). For anything shorter — like a 100m sprint — the number the chronograph hand lands on isn't the actual speed. It's what the speed would be if that pace held for a full kilometer.
How to Read a Tachymeter?
So there's one extra step: multiply that number by how much of a kilometer your distance actually is.
- Estimate your distance — a ballpark is fine. For a 100m sprint, that's 0.1 km.
- Start the chronograph the instant the event begins; stop it the instant it ends.
- Read the number where the hand lands. That's the "if this pace held for a full km" speed.
- Multiply that number by your distance to get the real speed.
Worked example: 100m in 12 seconds → the hand lands on 300 → 300 × 0.1 = 30 km/h, the real speed.
Tachymeter hand lands on
300
Actual speed
30 km/h
Actual speed = tachymeter reading × distance, expressed as a fraction of 1 km
What Is a Telemeter?
A telemeter does the opposite of a tachymeter: instead of measuring speed, it measures distance — specifically, the distance to an event you see before you hear it.
It relies on one physical constant: sound travels through air at roughly 343 meters (about 1,125 feet) per second, while light reaches your eyes almost instantly. That gap between seeing and hearing is exactly what a telemeter scale is built to measure.
How to Read a Telemeter, Step by Step
- Start the chronograph the moment you see the event — a flash of lightning, a starting gun, a distant explosion.
- Stop the chronograph the moment you hear the sound that followed it.
- Read the number on the telemeter scale where the chronograph hand stops. That's the distance to the event, typically in kilometers.
Example: The classic case — during a storm, start the chronograph on the lightning flash, stop it on the thunderclap. If 9 seconds pass, the telemeter scale reads roughly 3 km, meaning the storm is about 3 kilometers away.
Telemeters were originally developed for military and artillery use, letting soldiers judge distance to gunfire using nothing but sight, sound, and a stopwatch — long before laser rangefinders existed.
Fun fact: telemeters saw heavy use during wartime, helping soldiers judge the distance to enemy cannon fire by sight and sound alone.
Why TENJI Puts Both Scales on One Dial
Most chronographs commit to one scale — usually a tachymeter on the outer bezel, since it's the more commercially familiar of the two. Finding both scales on the same watch is uncommon enough that collectors specifically call it out.
TENJI carries its tachymeter and telemeter as a dual inner scale, set just inside the dial's edge rather than on the bezel, which keeps the 38mm × 13mm case compact while still leaving room for a date window at 6 o'clock and the flyback chronograph function of the Seiko VK64 mecha-quartz movement underneath.
A few details make the scales easier to actually use, not just look at:
- Full lume on every hour marker and hand, so you can still read the chronograph — and match it to the scale — in low light.
- Sapphire crystal with double anti-reflective coating on both sides, cutting glare so the printed scale stays legible in direct sunlight — exactly when you're most likely to be timing something outdoors.
- A sunburst main dial paired with a guilloché-finished sub-dial and matte bezel, so the functional scales stay visually distinct instead of blending into the rest of the dial.
Even the pushers carry the theme: both are stamped with the Yagasuri Wagara, a traditional Japanese arrow-feather pattern historically woven into kimono fabric to represent a straight, unwavering path — a fitting symbol for two complications built entirely around precision measurement.
Tachymeter vs. Telemeter: Quick Reference
| Tachymeter | Telemeter | |
|---|---|---|
| Measures | Speed (units per hour) | Distance to an event |
| Based on | Elapsed time over a known distance | Speed of sound (~343 m/s) |
| Formula | 3600 ÷ t | Distance = speed of sound × t |
| Typical use | Timing a vehicle over a measured mile, measuring an output rate | Judging distance to lightning, gunfire, or any seen-then-heard event |
| Reads accurately for | Events under 60 seconds | Any timed sight-to-sound gap |
Frequently Asked Questions
Can a telemeter measure speed?
No. A telemeter is built specifically to convert elapsed time into distance, using the speed of sound as its constant. For speed, that's what the tachymeter scale is for.
Do I need to do any math to use a tachymeter or telemeter?
No. Both scales are pre-calculated and printed directly on the dial. You only need to start and stop the chronograph at the right moments — the scale handles the conversion.
Why don't more chronographs have both scales?
Space. A tachymeter and telemeter both need real estate on the dial or bezel, and most chronograph designs only budget room for one. TENJI's dual inner scale is one way this combination fits on a wearable 38mm case without crowding the dial.
Wear the Measurement, Not Just the Time
Whether you're timing your commute, sizing up an approaching storm, or just enjoy watches that reward a closer look, TENJI turns a centuries-old measuring principle into something you wear every day. Explore the TENJI Chronograph and put both scales to work on your own wrist.
