I need education on the Thermoquad "staged accelerator pump" , that gives an additional shot when the secondaries open

found this in David Emanuels Carter Carburetors

the accelerator pump arm in the pic , you cant tell if the slot that is oblong as the pump linkage arm is in place is in place
in the pic the bottom hole looks like a circle, and you can see from the pic of the one I am familiar with, that it is slightly oblonged

or is it an optical illusion and they are both the same

if they are both the same, what am I not seeing that would provide an extra shot

OR

Is there different arm ?

is he using a wordy explanation to explain something that has been already happening that I am unaware of ?


pics comimg