The object of the Rulers... dialog is to allow you to draw objects in a scale on the screen that represents the size of the drawn objects in real life. If you have a machine part that is one foot high in real life and you wish to draw it one inch tall on the screen, you would set your scale in the Rulers... dialog to 1" = 1'.
The top ruler in the Ruler... dialog represents the size of the object on the screen. The bottom ruler represents the size of the object in real life. This is the 'actual' ruler.
Notice that you can set a scale in miles on the actual ruler. It would take a pretty darn big monitor to show that on screen!
The divisions per (actual ruler unit) has two purposes. First, it regulates the number of grid points per (drawing ruler unit) on the screen. The other is influencing the read out of the Location bar.
If you wish to have feet and inches, you need to check Fractional Read out and Roundoff values (see the record "Feet and inches displayed in Location bar).
If you check Zero point locked then you will not be able to move the zero point of the drawing while that ruler is active.
If you deselect Show unit name then the unit name or symbol will not display in the Location bar.