Two comments here:

You do not need a dark signal for that calibration. What you measure is the noise of the ADC. If you have dark signal in that image, it will shift the whole histogram to the right, and you might end up with a too low offset that clips for short exposures. So I'd rather recommend short(er) exposures for this. For histograms, you need to use logarithmic view to properly judge the proper cutoff.

And, as someone who does this calibration for all his cameras, I strongly second the request to make such a table (only) a recommendation, and not an automatic override (the most important feature of any automatics is the button to switch it off ;^>)

For implementation, I could imagine a (camera-specific) gain-offset table in the sqlite database that can be edited by the user (somewhat similar to the focus offset table for filters). Filling that one with recommendations on first connect might indeed be helpful for many users.

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