We choose the following rays emanating from the object in order to decide the position of the object. We keep the object on the principal axis in an erect position.
1. Ray from top of the object B towards the mirror, paraxially. reflects thru Focus.
2. Ray from top of the object B towards the pole of the mirror.
3. Ray from top of the object B through center C of mirror, retraces its path after reflection.
4. Ray from the bottom of the object A, along the principal axis.