The Boeing 707 and Convair 880 elevators were also tab operated (no PCU's) and could exhibit the same split on the ground dependant on wind effect as the DC9/MD80. The DC8 had the same basic control tab set up as the DC9 except that the elevator themselves were mechanically linked together and so moved in unison. The reason for linking them together on the DC8 was, as far as I could see, to provide a central point to install the old fashioned gust lock system Douglas had utilised.