When you log a watch's accuracy, you're comparing what your watch shows against what the real time is. WristLog gives you two choices for that "real time": your device's clock (the default) or a reference time synced from the WristLog server. The toggle lives in Settings.
TLDR: Should I turn it on?
If you see big deviations, check how often your device syncs time first and increase the sync frequency if you can. Windows, for example, defaults to a weekly sync, which admittedly isn't enough.
Turn the atomic time reference on if you fall into one of these:
- You've noticed your device clock is meaningfully off.
- You log from multiple devices that drift significantly from each other and want the numbers comparable across them.
If none of that applies, leave it off. Your accuracy numbers won't be different in any way that matters.
What "atomic time" means here
The WristLog server keeps its own clock disciplined to public atomic-time sources, syncing frequently enough to stay within a few milliseconds of true atomic time. Your device then syncs to the WristLog server.
The end result isn't atomic time. It can't be, I don't have an atomic clock. But it's as close as it can get.
Don't use "atomic time"
"Wait, all those superlatives about how accurate WristLog server time is and you're telling me not to use it?" That's right. I can do everything in my power to provide as precise a time reference as possible, but there's a middle man I cannot control — the network connection. You ask the WristLog server what the current time is and receive a response, but that response can be significantly delayed by network lag. There are clever algorithms in place that try to estimate that delay, but if your network connection is slow or generally bad, WristLog's "atomic time" can be more wrong than your device time. And that error will be different every time you ask. It's usually a few milliseconds, but on a bad connection it can be much worse.
That being said, every browser-based service claiming to provide atomic time suffers from the same network delay problem. This is not WristLog specific.
For most users, device time is fine. Modern phones sync their clocks frequently and are usually within a fraction of a second of atomic time — often as precise as a network-based atomic-time service can hope to be.
When it's useful
If your device clock drifts significantly and regularly, logging against that wrong reference quietly corrupts every accuracy number you record. Atomic mode bypasses this entirely by not using the time on your device.
It also helps if you log from multiple devices and want the numbers comparable across them. Each device's local clock is independent and may disagree with the others. Anchoring every record to the same server-side reference keeps your data consistent.
If all your devices stay within a reasonable deviation from "atomic time", you should still use device time.
How does WristLog compare to time.gov or similar services?
In practice, the difference between WristLog's reference time and time.gov is well under a hundredth of a second under normal network conditions. Both ultimately trace to the same atomic clocks; the only variation is in network paths.
If you're curious, you can compare them yourself: open WristLog's Reference Clock screen and time.gov side by side and check the deviation. You can't really know which one is closer to true atomic time, but for tracking a mechanical watch the difference is well below anything that matters — pick whichever you trust more.