A trip back to "the rock"

So today 4 of us went back to "the rock" where Zoe and I saw the mountain lion.  All the horses did fine.  I thought they would.  My info people told me that mountain lions rarely stay in the same place for more than 3 days.  Just in case we all kept up a good chatter, and walked up the hill.  We went to Inspiration Pt and stayed up there talking for a while.  While we were up there we saw a small plane flying very low to the water on the lake.  It was interesting...never have seen that before.
One of the people I went out with has the same GPS that I have on her phone...Endomondo.  We started the GPS about the same time--maybe 30 seconds difference--and we followed each other on the trail.  However the readings at the end were not the same.  Mine was 5.25 miles, hers was 5.  My average speed was 2.9 and hers was 2.75.  And none of the lap times were the same for the miles.  Interesting.  I came up with an idea (I can just hear a friend say "nerd") what happens when the one person takes both phones, starts them up at the same time so the phones are always doing the same thing at the same time on the same horse, and stop them at the same time---would the readings get closer?  Hmmmmm.