Timegrapher Readings Explained: What Do They Tell You About a Mechanical Watch?

What does it mean when a mechanical watch shows +27 seconds per day, 299° amplitude or 0.3 milliseconds of beat error? A timegrapher can reveal how the movement behaves during the measurement, but the figures need to be interpreted together.

At Østlandet Brukt & Antikk, we use a timegrapher as part of our checks on mechanical vintage watches. This guide explains what the readings show, what they do not establish and why one number is not enough.

What is a timegrapher?

A timegrapher listens to the movement's mechanical impulses. From their timing, it calculates rate, amplitude and beat error, usually displaying numerical readings and a graphical trace.

The measurement is a snapshot in a particular position and under particular conditions. It is useful for checking performance and investigating faults, but does not replace a full examination of the movement.

1. Rate: how much does the watch gain or lose?

Rate is normally expressed in seconds per day. A reading of +10 s/day indicates that the watch gains about ten seconds per day under those test conditions; -10 s/day indicates a loss.

A watch may read close to zero in one position and differently when lying or being worn in another. The test position and state of wind therefore matter.

2. Amplitude: how far does the balance swing?

Amplitude describes the balance wheel's swing and is expressed in degrees. It can provide information about energy reaching the balance. Movement design, winding, position, friction, lubrication and instrument settings all influence the reading.

There is no universal amplitude figure that classifies every mechanical movement as good or bad. The calibre, position and other test data need to be considered.

3. Beat error: the difference between tick and tock

Beat error is measured in milliseconds. It describes the timing difference between the two halves of the balance's oscillation, or how symmetrically the tick and tock fall around its neutral position.

A low figure is normally desirable, but movement type and the other readings still matter. Beat error is different from the number of seconds the watch gains or loses per day.

Three real OBA examples

• Certina DS-2 Bullseye: +27 s/day, 299° amplitude and 0.0 ms beat error.
• Certina Blue Ribbon Volvo: 0 s/day, 212° amplitude and 0.3 ms beat error.
• Longines Flagship, calibre 302: -54 s/day, 255° amplitude and 3.7 ms beat error.

These examples show why a zero rate reading alone does not tell the whole story. Equally, one high or low figure is insufficient for a confident diagnosis. The Longines readings are information to assess together, rather than hide behind a statement that the watch runs.

What do the sloping lines mean?

The timegrapher draws a trace from the impulses it detects. Slope and separation can provide further information about rate and beat. Unstable or scattered traces may prompt closer investigation, but should be read alongside the figures and knowledge of the movement.

Lift angle: an important setting

The instrument needs the movement's lift angle to calculate amplitude. The correct value depends on the calibre. An incorrect setting can produce misleading amplitude readings, so comparisons between tests should take account of how they were set up.

Can the instrument tell whether a watch needs servicing?

It can indicate abnormalities that warrant further checks. It cannot inspect dry oil, worn components, corrosion, old seals or previous repairs inside the movement. Attractive results during a short test do not document a recent overhaul.

A timegrapher test is not a service certificate

Tested on a timegrapher means the watch's running has been measured. It does not establish that the watch has been serviced, is water-resistant or is free from wear. Unknown service history should still be described as unknown.

Why do we test vintage watches?

A recorded measurement provides more information than simply saying that a watch runs. It gives us and the customer a clearer starting point for understanding performance at the time of testing.

The timegrapher is one of several tools. Visual checks, model and calibre identification, originality, functions and known service history remain important.

Buying or selling a vintage watch?

Read our guide to vintage watch value and the history of Certina DS. You can also browse available wristwatches.

Østlandet Brukt & Antikk buys, assesses and sells vintage watches and collections. Contact us with photographs and information if you are considering a sale.