Hello Tom,
you do not need to enter the calibration and distortion parameters manually in the application, you can write them in XMPs and load them along with the photos. You can find more information for example here:
https://support.capturingreality.com/hc/en-us/community/posts/115001359812-Importing-Camera-Calibrations?page=1#community_comment_115000616692
If you wish to import verified camera calibrations and lens distrortion coefficients calculated outside RC, then use the ‘Fixed’ option. Group images by calibration or lens if you know that a set of images have the same parameters, Rc will calculate the same arameters for the specific group of images.
In the 2Ds view, the principal point x and y are shown in pixels. In the Selected input table in the 1Ds view the principal point x and y are show in mm w.r.t. 35 mm film format. If you export the XMPs for the aligned images, you can see the relative offsets from the center of an image as PrincipalPointU and PrincipalPointV. The values in XMP are the values in the application devidied by 35 mm, therefore dimensionless. Do your images have the same calibration group (other than -1)? If yes, then these values should be the same for each image.
I am not sure what values “x = 1, y = 1, z=0.8” do you mean. You can find these exact values in the Alignment settings (if you use default settings) in the Camera priors table. However, those values specify the precision of the GPS coordinates in each axis.