The Anchor

The Anchor is where the hand is positioned on the jaw and the bowstring touches the face.
It is vitally important that the index finger is firmly placed against the jaw, the thumb is tucked into the palm of the hand so it can be placed firmly against the neck and the bowstring is firmly touching the chin (and nose, if possible.)
The relationship between all these positions is important as it acts as the rear sight, so it is vital that it be as consistent as possible.
It also acts as a consistent draw length position. Any variation in the position will effect the amount of force the bow will impart to the arrow.