thanks for the speedy reply.
I've owned the car for only a few weeks and I pay (almost!) constant attention to my pressure gauge. This is my first Merc though, so it's hard to know what to expect or to relate to, as the manual doesn't give you many pointers.
The reason I posted this thread is that this was the first time i'd noticed it going down to 1, probably because I've done only short trips/highway driving with it up until now. i.e., from what you say it would either be at 2 with the cold oil, or pegged at 3 on the highway.
I believe the numbers correspond to 15 psi or so steps?