OF DRAWING FROM RELIEF.
In drawing from the round the draughtsman should so place himself that the eye of the figure he is drawing is on a level with his own. This should be done with any head he may have to represent from nature because, without exception, the figures or persons you meet in the streets have their eyes on the same level as your own; and if you place them higher or lower you will see that your drawing will not be true.
Taken from The Notebooks of Leonardo da Vinci edited by Jean Paul Richter, 1880.