Reliable Time

[Jack T]

Wondering why people say cell phones are unreliable for timing a watch. I've seen where a cell phone, several in the same room on different services, a computer, an iPad and a cable box are all in perfect synch. In my home, in friends homes, in my office, even my AD/jeweler says to use it. I see many examples where several devices are in synch under various circumstances, so what is the basis for this assertion that cell phones are unreliable?

[powerfunk]

I wouldn't call them "unreliable," but the time can update/shift a few seconds here and there so they're not ideal for setting/measuring time down to the second.

[Ed Man]

Agreed. I check my watch against my iPhone all the time and I've also compared the phone and Time.gov and they are both spot on. And to be honest, being off a second or two is not the end of the world.

[kilyung]

There are several issues related to cellphone time accuracy. Here's just one...

https://code.google.com/p/android/issues/detail?id=5485

[Roller07]

They are just not as accurate as time.gov or time.is

Right now my cellphone is 5 secs fast and my computer is 27.6 secs fast.

[Tools]

Originally Posted by Jack T

Wondering why people say cell phones are unreliable for timing a watch. I've seen where a cell phone, several in the same room on different services, a computer, an iPad and a cable box are all in perfect synch. In my home, in friends homes, in my office, even my AD/jeweler says to use it. I see many examples where several devices are in synch under various circumstances, so what is the basis for this assertion that cell phones are unreliable?

All the sources you cite are updated from an over-the-air signal at various and unknown times.

If you set your watch to the source time, then a few hours later your "source" is updated, you no longer know what your watch is doing and your timing-test will be inaccurate.