I sewed a tape measure to my dark cloth. With camera ready to shoot, I measure the distance from the film plane to the lens. Example: that distance is 12 inches. Then I consider the focal length of the lens I am using. Example: Focal length 210mm, or 8.4 inches.
Now think f stops. How far apart are F12 and F8.4? Answer: 1 1/3-1 1/2 stops.
So I need to add 1.33-1.5 stops.
It works for me.
Would it be accurate enough for extreme closeups? Maybe not. Then I would ue the Caulmet exposure dial.