The Boris manual has (on page 6 of the version I have) the following:
"The rebreathers pressure/volume (PV) diagram is normally like a sideways ellipse,as you breathe out it starts from the bottom left and moves to the top right. The reverse is true on inhale."
Although I'm fairly sure I understand this (and the rest of the description) they do say that a picture paints a thousand words so I was wondering if anyone had the picture?
Ant S
could help you.