The PAM 40 is said to be a test watch for certain markets, was treated like a limited edition ( 200 pieces ) in a normal package, while the PAM 36 was a real limited edition ( 200 pieces, too ).
Titanium Grade 2, if my memory serves me well.
The 40 had a solid case back, at the contrary of the 36.
Same movement ( ETA manual winding ), and same year of introduction ( B Series: 1999 ).
While the PAM 36 was the true star with its 4 lines and brown dial, the 40 had a mysterious status. 2 different reasons to love both of them.