The Painter in oil

Draw straight lines across the study from each of the points, keeping them carefully
parallel, and seeing to it that the horizontal lines cross the vertical ones exactly at right
angles. These lines cut the study into right- angled parallelograms, which may be
squares or not according as the vertical lines are the same distance from each other that
the horizontal ones are, or not.
Number the spaces between the lines at the top, 1,2,3, etc., and at one side the same.
Now if you square off a part of your canvas with the same number of spaces at the top
and the same number at the side as you have done with the study, and keep the relation
of the spaces with the study, and keep the relation of the spaces the same, you can make
it as large or as small as you please, and you can draw the outlines within those squares
as they fall in the study, and they will be the same in portion without your having the
trouble working to scale. The squares furnish the scale for you, and the proportion is not
of the study to the picture, but as the vertical spaces are to the horizontal, in both the
study and the picture. By numbering the squares and canvas to correspond with those on
the study, and noticing in which square, and in what part of it, any line or part of a line
comes, you can, by drawing that in line in the same part of the corresponding square on
canvas, repeat the line in the same relation in with exactness, while still leaving the hand
free to modify it, or correct it.
In this way the simplest or the most complex, the largest or the smallest study sketch
or drawing may be accurately transferred to any surface you please.