A student places two alignment pins, $P_1$ and $P_2$, along the incident ray path. Suggest why the distance between pins $P_1$ and $P_2$ should be made as large as possible (e.g., at least 5.0 cm).

The perpendicular distance from the object pin to the reflective surface of the mirror is measured as $a=5.4cm$. By projecting the reflected rays behind the mirror line, the position of the virtual image is located, and its perpendicular distance to the mirror is measured as $b=5.1cm$. State whether these experimental results support the theory that the image distance is equal to the object distance. Justify your statement by referring to the measurements.

Describe one practical source of inaccuracy in this experiment, other than user error, that could explain why $a$ and $b$ are not exactly equal.