mountainlad...
i'm amused to hear you say ' estimated ground speed..'..
that was when i started flying....
now and again people will do it just for the hell of it...and of course students must still calculate estimated groundspeed...since, on flight tests, the use of DME ( distance measuring equipment ) which will also give a groundspeed readout or GPS, is not permitted ( except in the portion of the cross country devoted to a simulated diversion )...
otherwise..you do'nt have to calculate groundspeed any more since most people and/or aircraft now have GPS and get it accurately from that including ETA...( mores the pity maybe some would say)...but what a wonderful piece of kit GPS is...
gear up,
the dean.