# How accurate is your cell phone?



## Watchuseek Feeds (May 24, 2009)

This is a plea for help in conducting an experiment for the horological community. Many people compare the accuracy of their fine timepiece to the time on their cell phone. They, as have I, assume that this signal which is received from cell towers is accurate but it may not be so. I would like to compile some data as to the accuracy of these devices to help out the general horological community. Will you help me out?
Here is what you need to do:
For the next 5 days check the time of your cell phone compared to the time at www.time.gov
Download the excel spreadsheet here (right click and choose save as)
Fill in the values in the spreadsheet and email it to me at the end of 5 days.
Below is an image of the Excel Spreadsheet. Fill in the phone Make, Model, and Network Info. Visit Time.gov and compare the time on your phone with the time at the web page (sample image below) (circled in red). Fill in the error given (circled in blue). At the end of 5 days email me the spreadsheet. I'll fill it all in and let the community at large know how accurate our cell phones tend to be.
Note: If your phone doesn't show the seconds be sure to wait until the minute clicks over and record the time.gov time at the changeover.


CellTime.xls
P.S. Comments from those of you with first hand experience in the world of cell phones on accuracy would also be greatly appreciated.
Thank you.
  









More...


----------



## jackrobinson (Jun 11, 2012)

I use this site timeanddate to set my watches. It is independent of your PC. I found now that my celphone is completely synched to timeanddate although my pc which synchs with time.windows.com is 21 seconds fast.


----------



## lysanderxiii (Oct 4, 2006)

The cell phone is as accurate as the NIST time, just offset by -30 seconds....


----------



## gaijin (Oct 29, 2007)

lysanderxiii said:


> The cell phone is as accurate as the NIST time, just offset by -30 seconds....


Then why is my iPhone 4 on Verizon 1.48 seconds slow when compared to NIST time? :-s

Any info to support your statement?

HTH


----------



## lysanderxiii (Oct 4, 2006)

gaijin said:


> Then why is my iPhone 4 on Verizon 1.48 seconds slow when compared to NIST time? :-s
> 
> Any info to support your statement?
> 
> HTH


I don't use Verizon? Your iPhone may have a faster update connection than my little cell....


----------



## Triton9 (Sep 30, 2011)

I use iphone to set my automatic watch timing..


----------



## tonyphilly (Apr 3, 2011)

I use the app "ClockSync" on my Android phone to set my watches. It displays atomic time and compares to the phone time. It always shows the system clock on the android to be 15 seconds fast. I'm on verizon.

https://play.google.com/store/apps/details?id=ru.org.amip.ClockSync


----------



## gaijin (Oct 29, 2007)

lysanderxiii said:


> I don't use Verizon? Your iPhone may have a faster update connection than my little cell....


I'm sorry. When you posted this:



lysanderxiii said:


> The cell phone is as accurate as the NIST time, just offset by -30 seconds....


I thought you meant cell phones in general.

You must have meant just your cell phone in your experience, eh?

Thank you for clarifying.


----------



## James Haury (Apr 10, 2008)

Probably it is very accurate ,but I won't take it out of my pocket or pack to look at the time.I wear a watch on my wrist.It is much quicker and easier.


----------



## Monocrom (Nov 11, 2010)

Every cellphone I've ever owned was crap at keeping accurate time. I've owned everything from basic brick cellphones, (back when Verizon was still known as Bell Atlantic, and there was no time display) to small and handy but basic cellphones, to the early Smartphone models. None were accurate. My current phone is an old Samsung E-105. (I outgrew fancy cellphones with a bunch of useless apps. and battery-life measured in minutes instead of days.) It's off by about 5 minutes every two weeks. My car's clock is slightly better. I usually use my Citizen Eco-Drive model to reset both my cell and car timekeeping devices.


----------



## Drop of a Hat (Dec 16, 2011)

.07 seconds accd to time.is

Sent via Tapatalk


----------



## Turnaround (Jun 30, 2008)

My cell phone drops calls too often. That does not make it accurate to me. What else is a cell phone supposed to do... keep time????


----------



## gaijin (Oct 29, 2007)

I wasn't very happy with my response to the OP's question, so I spent a little time and came up with a better one. ;-)

I use an iPhone 4 with Verizon. I compared the time displayed on the built-in "Clock" app which came standard with the phone with the time on Time.is, my latest favorite time reference. I also recorded the offset between the iPhone's internal clock and NTP as reported by the Emerald Sequoia "Time" app.

Measurement of the offset of the Clock app with Time.is was done using the stopwatch method - start a stopwatch when the time reference hits a certain time and stop the stopwatch when the iPhone reaches a given number of seconds after the reference time and record the delta between expected number of seconds and actually measured number of seconds. This was done 5 times (Trials 1-5) and then averaged for a plot point.

The NTP offset was simply a recording of the value reported by the Emerald Sequoia Time app.

Here are the data:










And here is the graph with the blue line representing the time on the Clock app (which corresponds to the time displayed on the phone) and the red line representing the NTP offset as reported by the Emerald Sequoia Time app:










So if I were to have glanced at my cell phone for the time over the past 15 days, it would have displayed a time that was anywhere from a best of .19 seconds slow to a worst of 2.59 seconds slow.

Hope you find this info helpful.

HTH

ETA: I suspect the difference between the two times measured is because of an internal delay in the iPhone when processing its internal time for display.


----------



## cooma (Mar 14, 2014)

tonyphilly said:


> I use the app "ClockSync" on my Android phone to set my watches. It displays atomic time and compares to the phone time. It always shows the system clock on the android to be 15 seconds fast. I'm on verizon.


I have heard that this is caused by GPS signal. GPS-system has accurate time exept it does not update the leap seconds. Now it is 15 s wrong comparing to the official time.

I'm using NTP-program on my Linux and "Chronometer"-program on my iPhone.


----------



## pithy (Aug 22, 2010)

cooma said:


> . . . . . . . GPS-system has accurate time . . . . . . .


The constellation of satellites and earth based - hard wired facilities are fairly well synchronised. If any of the cell system relies on a satellite signal for indexing it she be understood that the timing of the receipt of the data packet is based in part on the length of the baseline but more importantly on the angle the satellite makes with the atmosphere relative to the receiver and the then current level of microwave refractivity. A subsequent multipath error renders the signal unusable. Hence the occasional errata.


----------



## BenchGuy (Sep 23, 2012)

An observation: On an absolute basis, cell phones (periodically corrected by satellite), atomic clocks (also periodically corrected), and even the downloaded screen from www.time.gov are going to be subject to inaccuracy from latency...if nothing else. The base CMOS clock is not really very accurate...hence the need for updating. My atomic clock claims accuracy of +/- 1.5 seconds depending upon its most recent update. However, using any of these standards to check timing on a mechanical watch is entirely adequate to confirm performance.

The necessity of a reference station for differential correction in precision surveying underscores the need to correct signal variation (DOD applied, as well as environmentally influenced).

That said, this will be an interesting excercise and data set. Look forward to the results. I would hypothesize that accuracy might be more location & acquisition method-specific than device-specific, however.

Regards, BG


----------



## cooma (Mar 14, 2014)

pithy said:


> The constellation of satellites and earth based - hard wired facilities are fairly well synchronised. If any of the cell system relies on a satellite signal for indexing it she be understood that the timing of the receipt of the data packet is based in part on the length of the baseline but more importantly on the angle the satellite makes with the atmosphere relative to the receiver and the then current level of microwave refractivity. A subsequent multipath error renders the signal unusable. Hence the occasional errata.


This is what I ment: (quote from Leap Seconds )



random web page said:


> The *Global Positioning System (GPS) epoch* is January 6, 1980 and is synchronized to UTC. GPS Time is NOT adjusted for leap seconds.
> 
> BEFORE THE 2012 LEAP SECOND: GPS-UTC IS 15 (GPS IS AHEAD OF UTC BY 15 SECONDS) AFTER THE 2012 LEAP SECOND: GPS-UTC WILL BE 16 (GPS WILL BE AHEAD OF UTC BY 16 SECONDS)
> As of 1 January 2008, and until the leap second of June 30 2012 TAI is ahead of UTC by 34 seconds. TAI is ahead of GPS by 19 seconds. GPS is ahead of UTC by 15 seconds.
> After June 2012, TAI is ahead of UTC by 35 seconds. TAI is ahead of GPS by 19 seconds. GPS is ahead of UTC by 16 seconds.


So it is now actually 16 seconds ahead of UTC.


----------



## pithy (Aug 22, 2010)

BenchGuy said:


> . . . . . The necessity of a reference station for differential correction in precision surveying underscores the need to correct signal variation (DOD applied, as well as environmentally influenced). . . . .


If with "DOD applied" you are referring to selective availability - it was turned off in 2000.


----------

