Question regarding the Contrast Sensitivity Function

Hi,

My question is about a plot of the Contrast Sensitivity Function I
found on http://www.webvision.med.utah.edu/imageswv/KallSpat24.jpg. I
read the corresponding article on
http://www.webvision.med.utah.edu/KallSpatial.html over and over again
but I think I still miss something: Can someone please explain to me
what the unit "Modulation threshold" on the y-axis of the plot means?

Thanks a lot for yout input!
Tim Allen

 

So this gives the measure for the minimum discernible difference in
gray scale level that the eye can detect. Is this right?

Tim Allen

 

So the y-axis values are the reciprocals of the minimum contrast
modulation that is still visible at a given frequency. I found another
article that states that if the CSF value is 200 at 10 cycles per
degree, it means you can detect a 0,5% contrast signal. - As my math is
bad, how do I calculate the 0,5% from 200?

Tim Allen