# Chronometer — Accuracy recording

> App to track mechanical watch accuracy against atomic time using photo capture. (iPhone/iPad app by Kilian Eisenegger.)

- Source: https://appshunter.io/ios/app/chronometer/id1562013733 (this page in markdown: same URL + `.md`)
- Developer: [Kilian Eisenegger](https://appshunter.io/developer/1333678887)
- Category: Utilities
- Price: $2.99
- Rating: 3.10/5 from 8 App Store ratings · 3 written reviews indexed
- Age rating: 4+
- Requires: iOS 18.6 · 3 MB
- Languages: American English
- Released: 2021-04-10
- Data updated: 2026-08-24
- Monetization: paid
- User reviews in markdown: https://appshunter.io/ios/app/chronometer/id1562013733/reviews.md

## What is Chronometer?

Chronometer – Mechanical Watch Accuracy

This app helps you track the real-world accuracy and long-term rate performance of your mechanical watch.
It provides an easy way to measure the daily rate of your watch against an accurate NTP time reference and to follow its performance over days, weeks or months.

Before starting a new measurement series, synchronize your watch with an accurate time reference. Do not reset the watch during the measurement period. An internet connection is required to obtain the precise NTP reference time.

How to measure your watch

1. Start the app and wait until the NTP server has synchronized. The NTP time turns green when the reference time is available.
2. Point the camera at the watch dial. You can use pinch-to-zoom and, on supported devices, the macro capability for precise reading of the seconds hand.
3. Tap the camera button to freeze the image. The app records the corresponding NTP reference time.
4. Read the exact time from the frozen image and adjust the displayed watch time using the picker wheels.
5. If desired, enter the current altitude above sea level.
6. Tap Save Rate to store the measurement.
7. Tap the camera button again to return to the live camera view.

For the best results, measure your watch once per day at approximately the same time. If more than one day passes between two measurements, the app automatically calculates the average daily rate for that interval.

Performance evaluation
The graph shows the daily rate of your watch together with the standard COSC limits and the more demanding COSC Excellence limits.
After at least 15 measurements, the app provides an additional COSC Evaluation based on the most recent 15 daily rate values.
The evaluation includes a COSC pass/fail assessment and a Concours Score from 0 to 500 points, derived from the chronometer competition formula.

The Concours Score does not include the thermal coefficient (CT). Temperature testing, controlled positional changes, magnetic exposure and shock testing cannot be reproduced during normal everyday use. The result is therefore not an official COSC certification, but a practical evaluation of the real-world rate performance of your watch.

The complete measurement history can be exported as a CSV file for further analysis. The exported data includes the date, absolute rate difference, daily rate difference and altitude above sea level.

Time reference: Swiss NTP server ntp11.metas.ch

The app also includes a COSC NTP 4 Hz reference dial for calibration and verification of optical timing instruments.

Requires iOS 18.6 or later.

## Key features

- Track daily watch accuracy
- Compare against atomic time
- Photo capture for time reading
- Altitude recording
- Save data in CSV format
- Analyze 15-day data trends

## Chart rankings

- #191 in Top Paid · Utilities (US App Store)

## Recent user reviews (3 of 3)

All indexed reviews: https://appshunter.io/ios/app/chronometer/id1562013733/reviews.md

### 1/5 — Scam of an app!

*2024-05-20*

Charges you to download the app. Doesn’t even give you the price before downloading. Save yourself 42.39

### 1/5 — Interesting Concept but Crashes

*2022-09-25*

I am using iPhone 12 Pro on iOS 15.6.1 and every time I hit “Save” the app crashes. Hoping for a bug fix.

### 3/5 — Not for clocks

*2022-06-22*

I was hoping to use this app to monitor long case clocks with 1 second pendulums. Can’t do it.  2.5 Hz is the lowest frequency.  Seems that would be easy enough to change.

## Frequently asked questions about Chronometer

### Does Chronometer have ads?

No, Chronometer does not contain advertisements. It is a paid application with no ads to interrupt your experience.

### What is the price of Chronometer?

Chronometer is available for a one-time purchase of $2.99.

### How accurate is Chronometer?

Chronometer relies on NTP servers for atomic time, providing a highly accurate reference. The app helps you measure your watch's deviation from this standard.

### What devices does Chronometer support?

Chronometer is optimized for iOS 16 and is available on both iPhone and iPad devices.

### How often is Chronometer updated?

The latest version, 1.8, was released on October 12, 2024. Updates are provided to ensure compatibility and performance.

### What is the age rating for Chronometer?

Chronometer has an age rating of 4+, making it suitable for a wide range of users.

### Can I export my watch accuracy data from Chronometer?

Yes, you can save your statistics data in Excel CSV format to your iCloud for further analysis. The CSV file includes date, absolute rate difference, daily rate difference, and altitude.

### What is the typical user sentiment for Chronometer?

Based on available data, Chronometer has a rating of 3.2 stars from 9 ratings, indicating a mixed but generally positive reception among its users.

## Version history (last 5 releases)

### 1.9 — 2026-08-20

What’s New

- New 15-day COSC Evaluation and Concours Score
- Improved camera with macro support and zoom
- Improved daily rate calculation for measurements over multiple days
- Optimized for iOS 18

### 1.8 — 2024-10-12

iOS 18 optimized
Small bug fixes

### 1.7 — 2023-09-24

Bug fixes for iOS 16
Bug fix for save rate

### 1.6 — 2022-10-14

Save Rate bug fixed

### 1.5 — 2022-09-27

COSC NTP reference dial for calibration of optical measuring instruments up to 2.5Hz
iPad camera view bounds fixed
iOS 16

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## More apps by Kilian Eisenegger

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All apps by Kilian Eisenegger: https://appshunter.io/developer/1333678887

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*Data collected daily from the US App Store and indexed by [AppsHunter](https://appshunter.io/). User reviews are verbatim App Store reviews. Ratings, prices and chart positions refresh continuously; this snapshot is from 2026-08-24.*