One more point here.
The accuracy of the GPS chipset is also important.
This has to do with how accurately the position that you are is calculated.
You will be surprised with the accuracy of GPS chipsets of phones... it can be 50-200m off !
Just imagine the effect it can have on a laptime.
That's why I personally laugh when someone tells me his laptime, which was measured with Harry's laptimer on an iphone
I see from the specs that the accuracy is 5m 95% CEP*.
That's mediocre in my opinion.
I bought
this GPS chipset a few months back, the position accuracy is 1.8m (10Hz update frequency). 39.95$