Tablet, phone, Roku, Computer clocks don't agree

The phone is part of the Sprint network although it also accesses my wifi. The computer, Roku, and tablet are all wifi devices on my home Comcast account. All are configured to set their clocks through their network and none of them agree. I could understand the Sprint device and the Comcast devices not agreeing, but no two of these devices show the same time. This isn’t much of a problem, just something that makes me curious. Any technoid sorts have an explanation?

Depends of a few things. Who they are talking to to get the time (although this shouldn’t matter.) How often they ask is going to be one issue. The standalone hardware clocks in most computing devices are by modern expectations woefully poor timekeepers. So you can expect discernible drift between the times they synchronize. Then you will get different behaviours depending upon the protocol they synchronise by, and the internal mechanisms used to get the clock back into sync.

Unix systems all tend to use NTP (network time protocol) to synchronise with a hierarchy of servers, and they use some carefully crafted algorithms to work out network delays. They can be expected to get your computer to within milliseconds of the correct time. Some Unix systems will use the network time to work out the drift rate of the local clock, and will calculate an offset rate, improving accuracy between syncs. I have Mac and iPhone - they are both Unix devices under the covers, and when I checked I could not discern any time difference between them - they were within one second of one another. One issue with syncing the time on a computer - they really don’t take kindly to time going backwards. If they have to be set backwards they will slow their internal clock and let themselves drift into alignment. Similarly jumping too far ahead will be handed carefully, to avoid nasty surprises. So a device that has been out of touch with the network for some time may take a while to come back into sync.

Mobile phones can also get their time sync from the cell. Cells need to have a very very good handle on the time, as many protocols are very time dependant. A simple phone, one with no major operating system issues underneath might be expected to synchronise immediately.

I have little idea how Microsoft handles time sync. In the past they have had a very naive way of managing time, and whether they have improved things, I don’t know.

I know some PVR devices sync once a day. They don’t need to be all that robust for the most part.

By how much do they differ? Fraction of a second? Many seconds? Exactly an hour?

The tablet is about six minutes ahead of the roku. The the phone and the computer fall between in what time they say it is. So, it is a few minutes difference from one device to another.

Does the tablet have cell service, or WiFi only, or never gets on the Internet at all?

The tablet has wifi service.

Unless this has changed recently, non-cellular Android devices (such as most non-Apple tablets) have no built-in time synchronization function. You can download third-party apps from the google app store to do this, BUT they will only do automatic clock setting if you root your device. (“Rooting” is similar jail-breaking on an Apple.) Google claims that automatic clock-syncing is a security issue of some sort. If you want to correct the time on your Android tablet, you need to do it manually.

Newer windows systems synchronize clocks once a week. If the synchronization fails for some reason (it often does), it gets rescheduled for 4 days later. There are utilities that you can buy that will schedule more frequent synchronizations for you.

I don’t know how the Roku works.

Windows - for quite a while, I’ve been running the freeware version of an old clock syncher, Tardis 2000, on a 24/7 machine with a web server on it. Configures as a service, and works fine as far as I’m concerned. Just be sure to turn off the Windows NTP handling if you are attempting to use it. If you PC is way off your phone, you probably aren’t or it isn’t working.

My PC agrees with my phone. Ya know, I haven’t paid too much attention to what time the Roku box says it is.

The screensaver I am using on Roku is a digital clock.

That can’t be true. I’ve owned many wifi-only Android tablets (I’ve bought 3 or 4 in the past year alone) and I don’t remember ever setting the clock on these, or ever seeing incorrect time on them.

I’ve never set mine either. It adjusts itself, including for daylight savings time or changing time zones.