"the sight-size method"

Working to the "sight-size" method means drawing the exact same scale and proportions as the object displayed.
I have been taught this approach by the Academy of Art of Florence. It helps me to achieve accurate proportions more easily, as well as to create a more exact visual impression of the subect on paper.
In the end, I draw what I see and not what I want to see.
In preparation, I can spend several hours trying to find the best position, the best light to give a more dramatic effect and to reveal the real  expression of my model.
For me, times does not matter !

Getting the true expression of the individual

When doing a portrait I seek to bring out both the fragility and the intensity of the individual, to reveal the real person. Accuracy is essential! A millimetre can make all the difference between a face that is young or aged, happy or sad, nervous or at ease with himself.
I am in heaven when I manage to capture the exact proportions and reveal the real person. 
But, like all amateurs, I must admit that I find difficult to recognise when I can go no further and decide that the drawing is finished

subtilities of shapes and shadows

If drawing is all about putting the right information in the right place, which is far more difficult than it sounds, I struggle sometimes to find ways of training my eyes to see the information accurately.
I spend a lot of time trying to see the relationships between shapes and shadows,  four or five hours minimum for each drawing. 
All the time, I keep forcing myself to see more accurately the subtilities of the forms, light and dark. I spend hours moving my eyes from one point to another on the cast/model and then moving my eyes between the same points on the drawing, making sure that the relationships between the points match.
Only once I decide the proportions look right, do I start to draw by the larger shapes, followed by the smaller ones. 
I must admit that, where possible, I get a third person to check my proportions  before I start working on the light and shadows!