Setting brightness level in copy/repro work using X-Rite colour checker

[Dinarius]

When doing copy/repro work, I set the overall brightness level of the image to the green value of the green patch on an X-Rite colour checker\- approximately, 150 RGB. (after black and white points have been established.)

I'm wondering how others who do copy/repro work arrive at a brightness level in processing?

Thanks.

D.