How the hell does the focus work on the Revere33 Stereo?

Well, the Revere 3 Stereo has a rangefinder. So there is the focusing.
At the top is a focus knob, surrounded by the depth of field disc. Focusing, in all cameras, is usually done by moving the lens back and forth. But in the Revere both lenses (Enna Chromar, quite simple) are solidly fixed to the front plate, and the wheels surrounding them are only for shutter speeds and apertures: there is no lens movement!
Maybe is the focal plane that moves? But I don't perceive any movement!
I would like to be able to lift the cover and see inside the rangefinder (and clean it), but I only see two screws at both ends, covered by the two knobs (which I cannot disassemble: removing the two screws on the body of them, the knobs remain stuck, not unscrew or lift).
But is it a fixed focus camera, and the rangefinder is a joke?
The mystery hovers over the Revere 33 Stereo ...
Can anyone help clear up the mystery? Thanks!

From a pdf I found online:

Focusing is via the Focusing Knob on the top of the camera which moves the focal plane. It was this feature that made it easier for the Wollenvere or Reverensak lens hacking mentioned later, as there was no focusing mechanism at the front of the camera.

Click to expand...

I’ve never owned one so I can’t comment. But in general there are three ways to focus the lens—move the lens forward or backward, move the film forward or backward, or internal focusing, i.e. move the elements relationship to each other. In this case, like the Mamiya Six, it sounds like it moves the film forward and back.

The PDF: