This is the Model from the Charles Bargue drawing set.
The first step is to block in the schema. The vertical plum line gives distance right and left, the horizontal plumb lines mark high points top to bottom. I measure with a knitting needle.
Continues to scrutinize the model and check the copy. Turn it upside down to see abstract shapes.
When an accurate copy of the schema is produced, take down the Bargue sketch and replace it with the fully rendered drawing. It is important to trace the reference lines onto the model.
Now put in the lines that accurately contain the "dark side" of the drawing.
Place the edges of the "dark" as identical as possible.
Once an "exact" copy, in two tones, has been produced, transfer the edges to the "good paper".
Keep pushing the edges until they match as exactly as possible.
Once the two tone drawing has been produced one begins to model the darks, reproducing cast and contained shadows. Turning the image upside-down will make it possible to see errors. One can work on the various edges, but don't start on values in the light side yet. The lines on the drawing are stretched strings. That way, once the drawing is finished there will be no marks from the lines.
Carefully measure and push to perfection the forms within the shadows. The tip of Agrippa's nose was especially fun. Once the darks are finished it is time to move on to the "lights".
Carefully measure and model the tones in the light of the figure. This adds the three dimensionality of the form. There is no end to the adjustments and refinements necessary to "copy" the model.
The "finished" copy.