The Wi-Fi-only iPad gets its time from an internal clock that, unlike Mac OS X, is not slaved to an external time standard. As a result, your iPad’s clock can drift, sometimes substantially, and some apps may be affected. Here’s everything you need to know: the cause, the impact and potential fixes.
3G iPads can get time signals from a cell tower and update their internal clock to compensate for drift. While cell towers can often be off by as much as 30 seconds, it’s usually just a few seconds. Owners of 3G iPads are in generally good shape in that regard. Unfortunately, the Wi-Fi-only iPad (and the iPod touch) is alone and helpless in the current version of iOS.
This Wi-Fi-only iPad clock drift is an issue for astronomers, laboratory workers, pilots, and other technical people who may be depending on the iPad’s clock because of other related technical apps they use that access that clock. Let’s look at the Mac first, by comparison.
How the Mac Does it
Your Mac knows how to connect, via the Internet, to what’s called Network Time Protocol (NTP) servers.
Mac’s NTP setting: System Preferences -> Date & Time
Apple even maintains its own NTP server that most Mac users connect to by default: time.apple.com. The communication protocol is for computer to computer connection on port 123, so it won’t do you any good to go to that URL with a browser, but if you want to see something human readable, you could go to sites slaved to the standard atomic clocks maintained by the National Institute of Standards and Technology (NIST) in Boulder, Colorado.
For example, you could go to the U.S. Naval Observatory to get a real-time updated clock for various U.S. time zones. (Shown below.) Unfortunately, the public NIST clock, www.time.gov requires Adobe Flash, and that’s unsupported on the iPad.
One of the USNO Time displays - via Safari
The iPad’s Problem
The problem is that the iPad doesn’t invoke the NTP protocol to adjust and maintain the internal clock. Worse, Apple won’t let third party apps access and update the clock, according to a developer I heard from. The iPad’s clock is simply left to drift.
All digital clocks are based on an oscillator. Depending on the quality of the oscillator, the temperature and other factors, the oscillator frequency may be off a little, and that causes the internal clock to drift in time. Apple iPad customers have seen some very large deviations, many, many minutes, from the actual time.
It is suspected, but not confirmed, that Apple has disabled the NTP protocol on the iPad to save the battery power needed to fire up the Wi-Fi radio periodically and connect to an NTP server. Wi-Fi may not be available at that very moment, and that would be a waste of battery power. Even connecting an iPad to a Mac or PC for a sync and backup doesn’t update the iPad clock, and that seems like an oversight.
Possible Fixes by Apple
There are solutions available that Apple could implement in an iOS update. It could update iOS to detect when there’s a sync going on and update the iPad’s clock with the Mac or PC clock, one that’s presumably connected to an NTP standard. After all, power is being supplied at that point. Or Apple could even detect when the iPad is being charged and sneak in an attempted NTP connection to update the clock. The time and bandwidth required to do that are modest. Perhaps Apple will get around to this in a future update. Of course, that spontaneous wake-up can’t happen if you’re on commercial airliner and in Airplane Mode. And there may be some other considerations, not mentioned here, that might have led Apple to permanently disable the iPad’s NTP client so that it doesn’t happen an an inopportune time.
Some apps that are time, navigation and astronomy oriented depend on the iPad’s internal clock. Examples are: Sky Safari, Star Walk, Nav Clock and VelaClock. If the iPad’s clock has drifted, they will give incorrect results also.
There is a very nice, free app from Emerald Sequoia, LLC called Emerald Time. It does connect to an NTP server (several, in fact) and will give you a very accurate time of day, likely within a second of the NIST atomic clock. It will even show you the offset (upper right, in red) from the iPad’s internal clock. Of course, you’ll need a Wi-Fi connection to the Internet for Emerald Time to work.
A leading minus sign on the offset means the iPad clock is fast.
As I mentioned above, Emerald Time can only show you how far off the iPad clock is and cannot make the adjustment itself. That’s up to you in the iPad’s Settings -> General -> Date & Time -> Set Date & Time.
Also, the Emerald Observatory and Emerald Chronometer use an NTP standard. I have reviewed Emerald Observatory here at TMO and highly recommend it. Unlike Emerald Time, it is not free, but it’s an absolute steal for US$0.99.
A Wi-Fi-only iPad, up through iOS 4.2.1, doesn’t have an automated mechanism for correcting the internal clock, and the iPad’s clock is not updated when connected to a PC or Mac. That internal clock can drift, so apps that depend on it can also have the wrong time. It’s up to the Wi-Fi-only iPad user to use Safari to go to a trusted time standard or to use an app that already has that feature built in. Then, the user will have to update the internal clock manually. And even then, the setting precision is only down to the nearest minute.