Oops. I must be undercaffeined (or is that undercaffeinated?) today - I just realised the OP has a Nettar 6x9 and not 6x6. Sorry.
The red distances on the 6x9 are a little tighter than the 6x6 but if used with care, they function just as well on either.
The 6x9 Nettar (at least the one I have) comes with an unusual left hand shutter button - the leather grip is also on the left side of the camera. An odd design, but one I was told years ago that was once common with German cameras from the1930s on. Can someone please verify this?
The elderly photographer who sold me my 6x9 Nettar told me the 105mm f/6.3 Novars were an "unusual: lens as when used wide open or at f/8, they have more limited depth of field than the 75mm versions but still produce excellent definition in negatives when used wide open. Obviously this was more important in the '30s through to about 1960 when most films were slower. Many old landscape photos in my family archives were taken with 120 or larger roll film folders (mostly now obscure Kodak and Ansco models as I was raised in Canada), and most of the contact prints I have show the foregrounds clearly out of focus.
As for lens quality, I have always held faith in the old saying (from the same photographer) that Zeiss never made a bad lens. Nor the makers of the Novar, possibly Rodenstock, Voigtlander or some other German factory producing quality optics.
Ste_S (#15), just set your lens at f/8, f/11 or f/16 and adjust the distances from the markings on the lens (ie the red dots). Novar shutters have clearly marked hyperfocal settings which can be briefly (and I hope correctly) explained as follows. If you are shooting at say, f/11, set the distances you want to get reasonably sharp, between the two f/11 markings to the left and right of the distance setting on the lens (the front part) and then set the speed to suit the exposure you want. Using the Sweet Sixteen rule, the best setting on a sunny day for an ISO 100 film would be 1/100 at f/16, but with f/11 you would be opening up one full stop, so 1/200 (which I believe the Nettar shutter has) would be your best bet.
Words are not flowing so easily with me today (I badly need another shot of espresso black or maybe a hefty slug of good Tasmanian Pinot) and I hope this explanation won't be too confusing...