I have uploaded a graphic to the FieldCamera eGroup files area that you can prin t, if you have a 1:1 printer w/accuracy, clip, put on your rail and find best fs top directly w/o measuring or math.
It's based on the table in Paul K. Hansmas article "View Camera Focusing".
Instructions are included in the graphic. Basically you just focus on near, mark rail, focus on far, then read best f-stop directly off of the scale. There are two scales one for near-far and one for far-near, use either one depending on yo ur technique.
There is a PDF, a Mac Tiff and a PC TIF.