Inverting Grayscale measurement scale

[Chemtech]

I'm working on making digital negative exposure curves for alternate photo processes.  Tutorials showing new curve creation using a step wedge show the step wedge scanned as 8-bit grayscale and loaded into PS, then the steps are measured using the Info window with white measuring 0% and black 100%.  I'm obviously trying to use GIMP and the grayscale measure tool measures the white step as 100% and the black as 0%.  Is there a way to invert the GIMP measurement scale so the white is measured as 0% and the black as 100%?  Or is Color>Invert the step wedge, and measure that, the only solution?
Thanks.
GT

[rich2005]

Keep looking in and maybe an expert will answer.

I looked at this https://afterness.com/digital/step_scale.html  and just a posterized gradient.

However,  taking this statement  quote Is there a way to invert the GIMP measurement scale so the white is measured as 0% and the black as 100%?

   

Using Colors -> Levels I can use the Black Point picker (1) to select white and the White Point picker (2) to select black
Then sent that to the Curves tool (3)  
..............but how that applies to your step-scale I do not know.

[Chemtech]

I guess I need to clarify my question:
I have a step wedge with 100 steps - from 0%(white) to 100% (black).
When I open it in PhotoShop and, using the color picker, InfoWindow indicates that the White 0% step has a reading of 0% on the Grayscale% scale, and the black 100% step has a value of 100%.

But if I open the same step wedge in GIMP, using the color picker and the info panel, it indicates the White 0% step has a reading of 100% on the Grayscale% scale, and the black 100% step has a value of 0%.
This causes some confusion and a lot of mental math, so I'd just like to know if there is a way to "invert" the Grayscale % scale so white 0% reads 0%, and black 100% reads 100%, like it reads in PS.

GT

[rich2005]

Gimp is not PS, you need to forget how PS works.  

You question is just about the posterized white to black gradient (aka ramp)

To change the scale in RGB mode then I assume that Gimp code and recompiling will be involved

However, if you set the color picker mode to CMYK then key (K = black) does show White = 0% and Black = 100%

Other tools
In addition, there are sample points, (1) White 0% and (2) Black 100% , you can move those around. The color picker (3) shows 50% here because the gradient is in linear mode, you can make a gradient in different modes. Another is the Pointer tool (4) can be more convenient than the color picker.