Proposed Canon
The Mathamancy Bracer is an Artifact. It is worn on the forearm, covering the upper part from elbow to wrist. Two straps hold it to the arm. The upper portion is similar to hard plastic and includes a spot where Parson's calculator watch can snap in.Erf-b1-p054 The watch is vital to its function: without the watch, the bracer does nothing.
The bracer instantly and effortlessly does raw calculations necessary to analyze probabilities and predict outcomes of battles - that is, Mathamancy.Erf-b1-p054 It is also capable of displaying Parson's current level, which in Parson's case, is invisible to other units. The user operates it by voice command.
- Two calculations on the strength of Gobwin Knob vs. hypothetical Archon attacks. These calculations were requested immediately after the deal was made.Erf-b1-p103
- One calculation on the odds of Gobwin Knob still standing after at the end of the current turn.Erf-b1-p105
- One calculation on the odds that forfeiting the eight remaining calculations would be a fair exchange for learning why the Archon units lost at Gobwin Knob now fight for Stanley. The calculation (a 4.14% chance of the exchange being worth it) led Charlie to refuse the deal. This calculation backfired: it taught Parson how to use his bracer to perform sophisticated calculations (and meta-calculations) on abstract future events.summer-updates-039
- One calculation on the odds that Parson is capable of casting the Carnymancy scroll Charlie gave him.LIAB 108 In this case, the bracer gave glitched results. An unidentified force tampered with the bracer, giving a chance of zero. However, Parson noted that the bracer briefly showed a different result. By asking the bracer to perform the calculations ten times in a row, Parson was able to see both results--0 and .980104773. Parson then blamed the false result as "railroad[ing] by two different GMs".
- One calculation on the odds that, had Faq not used the Turnamancy spell to end Gobwin Knob's turn, Gobwin Knob would have won the Siege of Spacerock and ended Jetstone's side.
Sizemore Rockwell hypothesizes that it may be an ArtifactErf-b1-p054. A broad estimate of the value is around 500,000 Shmuckers to the right buyer (a Side reliant on Mathamancy), the very value of the Summoning Spell including the casting and support package. Given that the Spell that created the Bracer was created by the residents of the Magic Kingdom, whether the Bracer qualifies by the strict letter of the definition of Artifact depends on the inner workings of the spell itself, something which we have not yet been made privy.
The effects of the bracer, when combined with Parson's calculator watch, effectively turns its user into a Mathamancer.
 Predictions about future
Parson's Mathamancy Bracer also seems capable of making sophisticated predictions about the futuresummer-updates-039 , so the Bracer may have Predictamancy abilities as well. (Or it is just really, Really powerful Mathamancy.)
- This is less predictamancy (foretelling a specific future event) and more extremely advanced mathamancy in the vein of oddsmaking/handicapping, though it certainly manages to calculate influences seemingly out of the mortal purview.
This definitely pushes the Bracer into Artifact category. It is essentially a Do-It-Yourself-instant-Mathamancer/Predictamancer. I don't think mere mortals have the power to do something like that. (At least as cost-effectively.)
 Real World References
Parson's Bracer may be based upon 1980's era calculator wrist watches, such as ones by Seiko: http://www.pocketcalculatorshow.com/nerdwatch/fun2.html