Also, with regard to the sign  of the value entered in the texture map- it is related to the sign defined in the offset node. If I move the feature in the other direction (-40 instead of 40) I need to reverse the sign in the texture map (from -0.8 to +0.8). Maybe it's what you meant, but I thought I could never use positive numbers at all in the texture map node.
It all makes sense now. Arnt math and the function editor wonderful!

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