P: Zone System Ansel Adams

If you set the Histogram to display values as percentages, it becomes even easier.

Zone I = 10%, Zone II = 20%, and so on.

 

The zone scale of Ansel Adams is mainly intended for people like me who work in black and white. It is composed of eleven zones from zero to eleven. By moving the mouse over the image, you can see which zone that part of the image belongs to.

The Zone System was developed as a means of previsualizing where various parts of the image will fall on the tonal scale in the finished print when working with black and white film.
It involves using a spot meter to obtain readings from the various parts of the image, and one stop difference in the readings will correspond to one zone difference.

Based on the readings, the photographer will determine how to expose and develop the negative to achieve the previsualized  result. (expose for the shadows and develop for the highlights)

I used the Zone System with large format film for many years, but I see no need for it with digital cameras – you can (at least roughly) previsualize the result directly in the camera.

I'm not sure why you need to work with the Zone System in Lightroom Classic, but the RGB readout you get from mousing over the image will give you a hint. If we say that zone I (solid black) is RGB 0-0-0 and zone X (pure white) is 255-255-255, you can use this table, which is not entirely accurate, but quite close.

Zone 0      0-0-0
Zone I       25-25-25
Zone II      50-50-50
Zone III     75-75-75
Zone IV    100-100-100
Zone V     125-125-125
Zone VI    150-150-150
Zone VII   175-175-175
Zone VIII  200-200-200
Zone IX    225-225-225
Zone X     255-255-255