Do the graticules in the curves editor have any absolute meaning?
The curves editor (in Adobe Camera Raw/Photoshop/Lightroom, probably all other image manipulation programs) has divisions along the X and Y axis. Do the values across those divisions have any absolute meaning?
For example some people claim that one square equals one stop. I strongly doubt that because notions like "a stop" only make sense when being scene referenced. The curve transformation would have to be applied in the input color space, but in general the photo editor is not even aware of the input color space. It's working in a device-independent working space.
Adobe Camera Raw might be an exception here because it has access to the device input profile, but I doubt it's doing anything different than Photoshop because the histogram displayed in the curved editor (and everywhere else) seems to have been de-linearized (TRC curve applied).
Also if Adobe Camera Raw would be working in device-dependent color space, and the gradations in the curve editor would have any scene-referened meaning, they would be different for every camera (because every camera has a different dynamic range), which is not the case.
If the gradations in the curve editor have no inherent meaning, how were they chosen?