Mathamancy Bracer is a Magic Item, possibly an Artifact, that Parson received in his second Stupid Meal.
It looks like a sleeve of hard plastic, but has a spot where Parson's calculator watch can snap into.
The bracer instantly and effortlessly does raw calculations necessary to analyze probabilities and predict outcomes of battles - that is, Mathamancy.
The effects of the bracer virtually turn its user into a Mathamancer.
Apparently it is an item of great interest to Mathamancy dependant factions like Charlescomm.