Thank you for all these tutorials. They're awesome and very helpful.

The way you're using sighting is actually the 'correct' way. Sighting is used to transfer accurate dimensions from the subject to the canvas.

When it is being shown only used when looking at the subject, they're not showing the whole technique, or else they're setting up for the classic joke of 'the artist seems to be painting the subject, but is actually painting his own outstretched thumb,