Universal Atmospheric Element Compensator
From Star Trek : Freedom's Wiki
The universal atmospheric element compensator was a significant contribution to bioengineering created at the Loonkerian outpost on Klendth. (Star Trek IV: The Voyage Home)
It is unknown what exactly this device does, but it is significant enough to be known by Spock. It can logically be deduced, however, that this device plays a role in terraforming and that it has something to do with the atmosphere.
