Kello 4+

Mechanical Watch Analyzer

Coldflower Design Corp.

Designed for iPhone

    • 2.8 • 5 Ratings
    • $9.99

iPhone Screenshots


Kello analyzes the precision of mechanical watches against the iOS system clock using a microphone.

How Kello works:

All mechanically regulated watches are designed to start and stop 1000s of times every hour. A portion of the energy used during this starting and stopping motion is released as acoustic energy, resulting in an audible "tick-tock" sound. The regularity of this sound can be measured against the more precise, internal time-signal of iOS devices, such as the iPhone, and the resulting difference in timekeeping is displayed by Kello.

Supported Watch Frequencies:

Kello can automatically determine the frequency of the watch being measured based on eight of the most common frequencies used in mechanical watches. These frequencies are standard among low-, middle- and high-grade mechanical timepieces and will accommodate the vast majority of mechanical watches produced in the past 100 years. The following frequencies are supported:

* 14,400 bph
* 16,200 bph
* 18,000 bph
* 19,800 bph
* 21,600 bph
* 25,200 bph
* 28,800 bph
* 36,000 bph

Recommended hardware:

Kello works best with an external microphone that has an excellent frequency response between 10,000 and 20,000 Hz.

How to know if your watch is mechanically regulated:

There are four simple ways to determine if your watch is mechanical and can be used with Kello.

1. Look at the text on your timepiece. If the word "quartz" is featured anywhere on the watch, your watch is not mechanical. If the words "automatic" or "shock-proof" are written anywhere on the watch, there is a very high chance that your watch is mechanical and its precision can be measured by Kello.

2. If your watch has a hand that indicates the seconds, observe how frequently it moves. If the hand moves only once every second, it is very likely that your watch is not mechanical. If this hand moves several times per second or appears to sweep along in a smooth, continuous motion, your watch is most likely mechanical and its precision can be measured by Kello.

3. Turn the crown, that is used to set the hands of the watch, while it is pressed fully in. If the crown turns smoothly, your watch is not mechanical. If you can hear a ratcheting sound as you turn the crown, your watch is most likely mechanical and its precision can be measured by Kello.

4. Place the watch close to your ear and listen. If you hear a noise approximately once every second, it is unlikely that your watch is mechanical. If you hear a constant ticking noise, your watch is very likely a mechanical watch and its precision can be measured by Kello.

What’s New

Version 2.49

This update addresses a critical bug when running Kello on iOS 14

Ratings and Reviews

2.8 out of 5
5 Ratings

5 Ratings

Jurgenkjurgen ,

Big improvement

This latest revision of the software seems to improve the ability to "lock on" to the mechanical signal a great deal. Even some quiet watches which could not be tracked with the case back closed can now be tracked simply by placing the microphone next to the case back. There is still a lot of drift as the program tries to interpolate the accuracy of the timepiece, but even this seems improved. I don't know if it is possible using the stock DSP plugins in the developer package and the stock microphone, but the ability to sense a beat error would be really really nice. For minor adjustments to the regulator this is very helpful, and with the update the efficiency is improved. If beat cannot be assessed with this technology I would be very happy just to have a system that locks on more quickly and gives a more stable instantaneous accuracy value. But this version is certainly worth the asking price, as it has saved me considerable time as compared to my previous technique of checking fine regulator adjustments using a clock.

Chemitso ,

Worked for me

I have an Oris Titan that I received as a gift around 2005. The watch has been slow (about 6-7 min a month slow) for years. I have sent it for servicing around 2007 (stripped crown) and then complete overhaul in late 2019. I mentioned it being slow each time but continued to be slow after service. I finally decided to open the back and see about adjusting it myself. The first adjustment wasn’t enough, so I adjusted it a second time this weekend Saturday morning, and for the first time ever it’s looking like it might be slightly fast. I have been just comparing it to my phone time daily, but thought it would be nice to check it with this app after reading about it. The watch back was already installed when I got this app later that night. At first it wouldn’t register, so I put the watch with half the case resting on the bottom of the phone with the watch back directly over the phone mic. I also had to put a clear glass mixing bowl over the phone and watch. Once I did that it read and analyzed the watch…+3.6 and then +4 on a second check. This seems to be what I am seeing after a day. Time will tell, but so far it looks like it works well. I have another watch running too fast. If I make any future adjustments to any watch I’ll check it with the app while adjusting.

Parallax3D ,

Don’t waste your money.

Unable to get a signal on any watch I tried. Don’t waste your money. There are better apps available.

App Privacy

The developer, Coldflower Design Corp., indicated that the app’s privacy practices may include handling of data as described below. For more information, see the developer’s privacy policy.

Data Not Collected

The developer does not collect any data from this app.

Privacy practices may vary, for example, based on the features you use or your age. Learn More


  • Family Sharing

    Up to six family members can use this app with Family Sharing enabled.

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