Want to use your new gray scale? Here's how.
Using Manual exposure mode, scan your printed gray scale to create an RGB file.
Open the file in Photoshop.
Select the Color Sampler tool.
Click once on the Black patch to set Color Sampler 1
Click once on the White patch to set Color Sampler 2
Click once on a Gray patch (any one in the center will do) to set Color Sampler 3.
Three samples are set, one for highlights, one for shadows and one for gray neutrality.
Open the Info palette, choose Window > Info
Color Sampler 1 should be 0R 0G 0B
Color Sampler 2 should be 255R 255G 255B
Color Sampler 3 should have 3 equal RGB values. Mine are 147R 147G 147B
The gray sample will determine if there is a color cast.
If the grey values are equal; the gray is neutral. 147R 147G 147B is a neutral gray.
If the grey values were 147R 147G 157B, I would have a Blue color cast.
If the grey values were 157R 147G 147B, I would have a Red color cast.
In any case, a Levels or Curves Adjustment Layer could be used to correct the color cast as well as the highlight and shadow points. Once a suitable correction is established, you can Save it for future scans.