Could someone please post a link, picture or explain now the Arca RM3D EVF works and what it looks like?
I am posting some pictures for you below. First, notice that the EVF has both portrait and landscape foot mountings to match the orientation of your back. Basically, Arca-Swiss provides three things with each lens that are unique to the lens focal length: (1) a focusing distance card (shown above by Terry), (2) a lens drum with DOF information that slides into the rear of the EVF, and (3) a numbered magnetic viewing mask with shift indicators that attaches to the front of the viewfinder.
Here is how the EVF works. The top of the EVF contains the information about which numbered viewing mask is required to be mounted based on the focal length of the lens and the format of your back (film or digital). The EVF "zooms" to the appropriate magnification as you can see from the pictures. Any focal length from 24mm to 210mm is set by aligning the focal length value to the bottom of the fixed top part (i.e., the rear/bottom part of the EVF is what moves to zoom the view), and then applying the appropriate mask.
The fixed front/top part shows what number mask is required for your particular digital back or film format. The leftmost column displays the range of digital back formats from 37x37 through 56x36 as well as film formats from 645 through 4x5. The rightmost columns correspond to the range of focal lengths. As an example, look at the image showing the top of the EVF fully extended. If you wish to use a 50mm lens and a 48x36 format back, then you would need to attach viewing mask #7. Or, if you wish to use a 210mm lens and a 48x36 back, then you would need to attach viewing mask #9. If you want to use a 35mm lens and a 48x36 back, then you would still use a #7 mask but you must also zoom the EVF by sliding it forward so that the 35 mark appears just below the fixed top part.
Once the EVF focal length is set for your lens/back combination and the appropriate mask is attached, you can then compose your image. A shift composition is performed by sliding the mask up/down/left/right on the EVF. The mask contains small "holes" in it that can be seen when looking through the EVF. Each "hole" that you see in any x-y direction corresponds to 5mm of shift. For example, if you compose your image and see 1 hole visible on the bottom of the EVF and 2 holes visible on the left side, then you would then shift the rear of the RM3D by 5mm downwards and 10mm to the left (opposite direction as the mask) in order to match the back to your viewing composition.
Once your image is composed, then you set your aperture and focus by measuring distance. For example, you can take a distance measurement with a laser meter. Then, you choose your f-stop based on your desired DOF from the lens drum. The lens drum (see the attached picture) contains DOF information based on the shooting distance and the f-stop for the lens being used. Finally, you focus the lens by using the focusing distance card, which indicates the appropriate RM3D helicoid setting based on the measured distance. Of course, shutter speed and iso are set according to the lighting conditions.
That's it. I explained this perhaps with more detail than necessary, so it might sound complicated, but in fact this procedure all takes place as fast as your ability to compose the shot. However, to get really accurate focus, you must calibrate your lenses with your backs and create your own focusing distance cards and DOF information. This is a one-time-per-lens-per-back effort. This is what I did with my lenses and backs, and you can see the amazing accuracy that I now get from the test shot I posted the other day, without moving the digital back at all, i.e., without shooting tethered, without using a sliding back and without any ground glass focusing.