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?