What a timegrapher measures.

A timegrapher is a small machine that listens to a watch ticking and turns the ticking into three numbers. Those numbers tell you how the watch is performing. Every finished watch at the bench sits on one before it leaves. This is what each number means.

What a timegrapher actually is

A timegrapher (in some workshops still called a "watch rate machine" or "timing machine") is a piece of test equipment with a sensitive microphone, a microcomputer, and a small display. You clamp a watch into a microphone holder, the microphone picks up the watch's ticking through the case, and the machine analyses the timing of those ticks to report how the watch is running.

The most common timegraphers in modder workshops are the Chinese-made Weishi 1000 and Weishi 1900 series. Professional Swiss watchmakers use Witschi or Greiner instruments at five to ten times the price. The Weishi units are perfectly accurate enough for any hobby modder's needs — they read the same data with the same precision, just less polished in the user interface.

The three numbers

Every timegrapher reports the same three things, regardless of brand. Once you understand what each one is telling you, you can read any timegrapher screen anywhere.

1. Rate — seconds per day

The rate is how many seconds the watch is gaining or losing per day. It's the primary number you care about as a wearer. A positive rate (e.g. +5 s/d) means the watch is running fast and gaining time. A negative rate (-12 s/d) means it's running slow and losing time.

The Seiko NH35 leaves the factory specified at -20 to +40 s/d — Seiko's quality control tolerance, not what you should accept. A regulated NH35 should settle within ±10 s/d easily; ±5 s/d with care. The rate is the number you adjust with the regulator lever on the balance bridge.

2. Amplitude — degrees of swing

Amplitude is how widely the balance wheel is swinging on each oscillation, measured in degrees. A balance wheel that swings 180° from its rest position would have amplitude 180°; one that swings further to the left and right of rest is at a higher amplitude.

Amplitude tells you about the health of the movement. A high amplitude (within reason) means the mainspring is delivering proper torque and the escapement is efficiently transferring energy to the balance wheel. A low amplitude means something in the chain — mainspring, gear train, escapement, or balance — is sluggish or worn.

For a brand-new NH35 fresh from Seiko, amplitude should sit around 280–290° dial-up. If you're seeing 220° on a fresh build, something is wrong: either the mainspring isn't fully wound, the movement is dirty, or a part is binding.

3. Beat error — milliseconds of asymmetry

Beat error is how asymmetric the balance wheel's swing is around its rest position. Ideally, the balance wheel swings exactly the same distance to the left as it does to the right of centre. If it's swinging more in one direction than the other, the ticking sounds slightly "limping" — tick-TOCK, tick-TOCK — rather than the even tick-tick-tick of a properly balanced watch.

Beat error is set by physically rotating the hairspring stud (the point where the outer end of the hairspring attaches to the balance bridge). On most modern movements, including the NH35, this is done by lifting and rotating the hairspring collet by a tiny angle — a delicate operation that most modders leave at the factory setting. A beat error of 0.4 ms is fine for hobby use; chasing it below 0.2 ms is professional territory.

How the timegrapher actually measures these

The microphone in the timegrapher picks up the audible ticks of the escapement. Each tick is actually two distinct sounds: the impulse (the pallet stone releasing a tooth of the escape wheel) and the lock (the next pallet stone catching the next tooth). The timegrapher records the exact time of each sound to the microsecond.

From the precise spacing of those sounds, the timegrapher calculates:

• Rate — by comparing the actual interval between ticks to the expected interval (1/6 of a second on a 21,600 BPH watch). If ticks are slightly closer together than expected, the watch is running fast.
• Amplitude — by measuring the time between the impulse sound and the next lock sound. A wider swing means a longer time between those two events.
• Beat error — by comparing the timing of left-to-right swings versus right-to-left swings. Asymmetry shows up as one pattern being shorter than the other.

Modern timegraphers also display a visual "trace" — a graphical line that shows the rate over time. A horizontal trace means the watch is running consistently. A trace that drifts up or down indicates the rate is changing over the measurement period. Two parallel traces (one above the other) indicate the beat error. Dotted or scattered traces indicate the microphone is picking up noise or the watch has an intermittent fault.

The position test

A mechanical watch behaves differently in different physical positions because gravity affects the balance wheel asymmetrically. The five standard test positions are:

• Dial up — watch lying face-up. Usually the position of highest amplitude.
• Dial down — watch face-down. Similar to dial up.
• Crown left — watch on its side, crown pointing left. Vertical position.
• Crown right — watch on its side, crown pointing right. Vertical position.
• Crown down — watch upside-down, crown pointing down. The most demanding position.

A well-regulated watch holds rate consistently across all five positions. The difference between the best and worst position is called positional variance. On a good NH35, positional variance should be under 15 s/d. On a chronometer-grade watch, under 5 s/d.

At the bench we test every watch in at least the dial-up and crown-down positions before regulation. If positional variance is wide, the movement may need finer adjustment (the regulator can only correct the average rate, not the variance).

"A watch that's never been on a timegrapher is a watch whose rate is unknown. That's not a watch you can trust."

How regulation actually works

Regulation means physically adjusting the watch to bring its rate closer to zero (no gain or loss). On the NH35, the regulator is a small lever on the balance bridge with markings "+" and "-" on either side. Moving the lever toward "+" speeds the watch up; toward "-" slows it down.

The lever works by changing the effective length of the hairspring. The regulator has two small pins (or a pin and a flat) that grip a section of the hairspring near its outer attachment. Sliding the regulator effectively shortens or lengthens the active portion of the hairspring. Shorter hairspring = stiffer = faster oscillation = faster watch. Longer hairspring = softer = slower oscillation = slower watch.

The adjustment is sensitive. On the NH35, a movement of half a millimetre on the regulator lever changes the daily rate by roughly five to eight seconds. Adjustments are made in tiny increments, testing on the timegrapher after each one, until the rate sits where you want it.

Why this matters for a finished watch

A watch that's never been on a timegrapher is a watch whose rate is unknown. It could be anywhere from +40 to -20 seconds per day (the Seiko factory tolerance). The watch will keep working — but it could drift by minutes in a week, hours in a month, days in a year.

A regulated watch is one whose rate has been measured and brought into specification. The wearer can trust it. They can sync it once a week against their phone and the watch will hold within a few seconds.

This is the single biggest reason to assemble a watch at a bench rather than from a kit alone: without a timegrapher you can't regulate, and without regulation you can't tell what the watch is doing. The cheapest acceptable timegrapher costs $200+ AUD. The bench includes the regulation as part of the class.

What to do if your timegrapher shows trouble

• Rate way off (e.g. +45 s/d) — adjust the regulator lever. Move it small amounts and re-measure.
• Amplitude below 240° — mainspring may not be fully wound (try 30+ turns of the crown), or the movement may have dirt/old oil affecting the escapement.
• Beat error above 0.5 ms — the hairspring stud needs adjustment. This is delicate work. Most modders leave it at factory and accept the small error.
• Trace scattered or noisy — the microphone may not have a clean signal. Reseat the watch in the holder, make sure the case-back is closed properly, try again.
• Trace drifting — the watch's rate is changing over time, suggesting an intermittent issue. May resolve as the movement settles in (run for 24 hours and retest) or may indicate a problem.

At the bench

We run a Weishi 1900 timegrapher and test every finished watch in at least two positions before it leaves. We aim for ±5 seconds per day in dial-up, with positional variance under 15 seconds per day. If we can't get a watch into that range, we either rebuild or replace the part causing trouble — the student doesn't leave with a watch that doesn't work.

If you're modding alone and you don't yet own a timegrapher, get one before your first finished build. They're cheap. They're the difference between making a watch and assembling a pile of parts that ticks.