Karl - what are the x axis markers that you want to be an inch apart? Do you mean that if the x-axis has ticks of 0,1,2,3, etc. then these should correspond to differences of one inch? Please describe in more detail what you are displaying on your axes that you need to show it in inches.
Also, clarify what you mean by how do I make the slider react to the axis? What does your slider do, and how should it affect the axes?