Wikipedia
Nieh-ching-t'ai
Nieh-ching-t'ai is a mirror in the Chinese underworld. It is also known as the Mirror of Retribution or the Mirror of Past Existences.
Souls are forced to stand in front of it and see their true selves, namely the events of their previous existences. The Yama King then makes his judgment.
It stands in the Court of the First Yama King and faces to the east, on a raised stand eleven feet in height. The mirror has a circumference of six feet.