In {HEAD ~ another implementation}, {TAIL ~ the second mobile device} could also optionally present a distance to the first mobile device 
In { HEAD ~ another implementation } , { TAIL ~ the second mobile device } could also optionally present a distance to the first mobile device
OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH