I'm just trying to get my head around electromagnetics for the first time, and need help understanding a question that asks: "Using BH curves find the maximum permeability of the cast iron forming the magnetic path." Now from wikipedia I know that the permeability of cast iron should be around 0.25H/m. What I don't understand is how to get this quantity from a B-H curve like this one: http://imgur.com/eiv6IuN Now what I do understand is that permeability is given by B/H essentially. That would imply it is the gradient of these lines. So to find the maximum permeability all we need to d is find the point with the most positive gradient. Is this logical correct?