Colorimetric Reproduction In Capture One 12

load the Raw capture of the ColorChecker SG in C1 12, select Linear Response curve
Set Levels so that the whitest white is around 250
Export TIFF with embedded profile, click on Process
It doesn’t matter what profile is selected!
Load the exported TIFF in input 5. You can see the camera name in the profile name.
Create a profile and see the resulting ∆E, click on REPORT to get a detailed report.
Relaunch Capture One and select the new profile.

For the most accurate reproduction pick Absolute in the Preferences. Now process the image to the Working Space of your choice, e.g. AdobeRGB or ProPhoto.