Joshua, the 360FGZ unit will work with Z1-p in plain TTL mode, which doesn't allow flash compensation (as opposed to P-TTL, available only with MZ-S and later bodies). So the answer is adjust the output from the body.
Servus, Alin Joshua wrote: JH> I am using these two pieces of equipment together and want to JH> underexpose the flash by one stop (TTL). This flash unit allows you to JH> adjust the exposure from the back, but the Z1-p adjusts the output too. JH> Where should the adjustment be made? Flash - Body?