[grommi]

Obviously, ostensibly at least, it seems the OP has erred with the twenty centimeters, but has he really?

He just might be talking about the actual item photographed being off of by such amount (almost eight inches, avoirdupois-wise). In other words, if he is taking a picture of a person's head, that head's image in the negative will be 'off' by an amount equivalent to 20 cm from the actual head's center. In other words, when he thought that the top of the head was flush with the top of the viewfinder, the head was actually an equivalent of eight inches LOWER in the negative. Of course, it is NOT eight inches lower in the actual negative, but only with regard to the original scene.

No, the OP has not erred with the 20 cm and to say it again clearly, it's NOT a parralax thing of the viewfinder but a distance metering thing of the rangefinder.

Anyway, so far obviously nobody knows how to fix that (calibrate the rangefinder) with household resources, so I stick with guessing the distance. But the real sense of a rangefinder is another one than guessing .....

Best - Reinhold