To the OSIsoft Learning folks:
You may want to revisit the diagram shown starting at instant 4'32" of the video "OSIsoft: Exception and Compression Full Details" in the OSIsoft Learning Chanel on YouTube (as well as in the course materials of the "PI System Architecture, Planning, and Implementation" training and any others where it might be used), as the diagram shown in the Compression Testing section of the PI Server System Management Guide is a little different:
As you can see, the PI Server System Management Guide describes the geometric shape related to the swinging door compression algorithm as a paralelogram (not a rectangle) and the CompDev attribute of the PI tag as half the size of the vertical sides of the paralelogram.
Edit: for accuracy.