Timegrapher X is optimized to work with the original Apple EarPods and relies on the high-quality headset microphone. Although there are many replicas available, they are often unable to capture the high frequencies required for watch recording. The difference can be huge. TBA: mic comparison video
High-frequency sounds, sometimes produced by electronic equipment, can be hard to hear — or even inaudible. Even so, they can interfere with the recording, as the app actually works in the high-frequency range. Sometimes, you can have much better results in another room or building for no apparent reason.
Some watches are louder than others. Having a louder watch near the watch under test can affect the results, as the app may pick up the wrong ticking sound. Always keep loud watches and clocks at a distance, preferably in another room. TBA: video showing the effect
When using the app while the iPhone is charging, the power adapter can introduce various noise disturbances that bleed into the signal recorded. It is always better to make measurements with the iPhone fully charged and disconnected from the power adapter. For longer test durations, a power bank or a wireless charger can be used.