A bit pedantic, this discussion, I think. It's pretty obvious that we are talking about changes in the observed IAS during a stall, with Vs as a reference.. .. .Some factors not yet mentioned:. .. .</font><ol type="1">[*]<font size="2" face="Verdana, Arial, Helvetica">Ground effect</font></li>[*]<font size="2" face="Verdana, Arial, Helvetica">Formation flight</font></li>[*]<font size="2" face="Verdana, Arial, Helvetica">Damage to the wing</font></li>[*]<font size="2" face="Verdana, Arial, Helvetica">Compressibility</font></li>[*]<font size="2" face="Verdana, Arial, Helvetica">Climb/Descent angle</font></li>[*]<font size="2" face="Verdana, Arial, Helvetica">Boundary layer control devices ("blown" wings and vortex generators)</font></li>[*]<font size="2" face="Verdana, Arial, Helvetica">Vectored thrust</font></li>[*]<font size="2" face="Verdana, Arial, Helvetica">Gusts</font></li>[/list=a]<font size="2" face="Verdana, Arial, Helvetica">