[time-nuts] Smart Phone time display accuracy...?
albertson.chris at gmail.com
Fri Mar 17 17:38:17 EDT 2017
> AndroiTS GPS Test (V 1.48 Free) is good, but a battery hog I find. On
> my Moto G, I find that it can handle not only the US GPS system, but
> three other systems too, including Glonass, and I think the new Chinese
> system. I don't recognise the last symbol, maybe Galileo. Not bad for
> a consumer gadget.
THIS is why the phones don't really track time so well. Not that they
can't but doing so requires battery power. It would need to keep
receivers and internal oscillators powered up full time. These
phones have an incredible degree of fine grained power management.
Processors can slow their clocks, graphic units can power off. The
best clocks required stable conditions and even temperature controlled
ovens for their crystals.
Bt the question raised here was more interesting: How accurate is the
DISPLAYED time. No need for an internal probe you can look at the
screen. The problem is that human eyes are not good at this and I
doubt anyone could detect even a 100 ms error. You need to rig up a
photo detector aimed at the screen.
One question was if the software stack from GPS/Cell receiver to
screen added any delay. Of course it does but did the designers
account for any fixed delay? You have to measure to know.
Only one manufacturer, Apple seems to give a worst case spec and they
only give it for a phone pared to a watch, 50 ms. But it might be
much better. I guess it is most of the time. Again, to answer what
was asked, you'd need some kind of optical sensor.
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