Originally Posted by
oldoberon
But if 3rd hourly ping is at the same reduced spacing to the 2nd one , as the 2nd one is to the 1st one that constant spacing tells you it is on a constant heading/trk but nothing about that heading or track.. Do you agree that?
Well no, actually. If the spacing between arcs 1 and 2 is less than the distance that the aircraft is likely to have flown in the hour, that tells us that the average track angle was somewhere between radial and tangential. If the spacing is the same between arcs 2 and 3 then there are at least two average track angles that would result in the same flight distance (more if we allow for possible differences in groundspeed, but let's discount that).
Now you may think that is unimportant or of no use others will disagree a) it is an extra known and B) in IMHO it indicates a flight south, constant track north is eventually going to be spotted by the ground or another aircraft visually.
Why north or south in particular, rather than any other possible direction?