If any creature within 10' of this magical abacus speaks a mathematical formula involving numbers aloud, the abacus' beads slide and clack about for a round, and then a ghostly voice speaks aloud in the same tongue that the question was asked, giving an answer. However, the answer is wrong, and the abacus of miscalculation includes a subtle enchantment such that listeners believe the answer. (A creature that might notice the inaccuracy must succeed on a DC 13 Intelligence saving throw or think it made a math error itself.)