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Generally, you think of a stopwatch as a simple mechanism that just measures how much time has elapsed. In other words, it’s a device or app that “counts seconds.” And the stopwatch app on your iPhone does work like that, but there’s a small quirk that’s really interesting to note.

Instead of just counting the seconds after you tap on Start, the Stopwatch app actually records the time and date that you hit that button.

It then saves that start time and calculates the amount of time that has elapsed since then.

The end result is that the Stopwatch can measure time, even if you close out of the app or you shut down your phone. It doesn’t need to know how much time has passed because it can simply calculate it on its own. (The timer, of course, works in a similar way, just in reverse.)

That’s pretty much the reason that your stopwatch can go for days without any error in calculations. You’ve probably forgotten about it at least once and returned to see a massive number on the display.

Once you know that one little detail, the next thing that may come to mind is just how far you could push those limits.

While there’s no official world record for most time logged on an iPhone stopwatch, there are some unofficial results. Joshua Mallik of Kuwait City, for example, apparently logged about 9 years on his iPhone. That roughly translates to 78,888 hours and 32.80 seconds.

There is, in fact, a number of people who apparently just leave their stopwatch running to achieve similar records.

In any case, the stopwatch on your iPhone is a handy tool to track time and events. And with this little tidbit of knowledge, you can rest assured that you’ll be able to accurately track time — even through iPhone resets or your battery dying.

It’s worth noting that the Apple Watch stopwatch probably works slightly differently. At the very least, Apple notes that the maximum amount of time it can run is 11 hours and 55 minutes.