Yes, to estimate distance using a COUPLED rangefinder type of focusing, getting images in line with each other. And once the images are in line with each other, it is exactly, exactly, the same distance as determined by a real rangefinder, at any aperture. Pretty cool then for a camera that is not a rangefinder and just using mirrors. This however led to the confusion, plus the fact that Hasselblad calls their focusing screen a Split-Image Rangefinder -
http://www.calumetphoto.com/item/HA3244.html.
This is for my particular configuration at least, since it may be different with others, as explained in the other posts here since theirs go dark and affected by aperture settings, and mine doesn't. It probably is because of the PME-45 viewfinder I use which is the latest, although just recently discontinued, or maybe the camera model - still waiting for Hasselblad's reply. This is why I asked if others had the same configuration.
If it did go dark at different apertures, I would have sold it a long time ago, like I am selling my Yashica GSNs I bought 2 weeks ago after I change their light seals, I can't stand the dark viewfinder (great pictures, though, but not my type of viewfinder).
Well, thanks to all for all the clarification here. It certainly is not a rangefinder in terms of mechanism, I accept that. There really is more to a real rangefinder than just combining images in a viewfinder and getting the distance.
BTW, finder, that is a great picture in your avatar ...
.