Mathematics is calculation and formal reasoning. A Reasoning test suffices for counting and for feats of memory; Mathematics is what solves an actual problem, and a Mathematics Success Value test establishes how far up the ladder of complexity the character can reach.
| SV | Problem | SV | Problem |
|---|---|---|---|
| ≤ 0 | Counting | 7 | Geometry |
| 1–3 | Arithmetic | 8 | Trigonometry |
| 4–6 | Algebra | 9+ | Probability |
Direct uses arise rarely in play. What Mathematics mostly does is stand behind other skills as a Secondary Roll or a required competence: the measures and proportions of an alchemical formula; the geometry and probability an astrologer’s calculations rest on; the account books and exchange arithmetic of a merchant; the dead reckoning of a ship’s pilot; and the structural sums that turn an engineer’s inspiration into a buildable design.
Logic. Mathematics also stands for formal training in reasoning. Where a Reasoning test would be made to analyse something — particularly anything involving design or conceptualisation — a character may substitute Mathematics if their Mastery Level in it is higher. This is not permitted for every Reasoning test; recall and intuition remain Reasoning’s own.
Cyphers. Important messages are often disguised, sometimes elaborately. Designing one follows the ordinary rules for composing a document, with the author’s Mathematics Index as the subject; a practical code is usually short, so its length reflects intricacy rather than volume. A recipient holding the key reads it automatically on a reading result of at least SV 3. Without the key, the reader rolls a number of d10 equal to the Value Diamonds of their reading result against a Target Number equal to their own Mathematics Index, and breaks the cypher only when their successes at least equal the insights the author worked into it.