Ruling Pen
A fluxionist's drafting pen: at a Reckoning Desk it draws the channels of riverbed puzzles, one segment for one division of ink. Refill it with an ink sac and any current shard on a crafting table.
kinditemcreative tabFluxion
Currents
Gloom1What the Loupe reads: 1 in all. The game works them out from its recipes. Wheel of Currents
In the Codex
Entry 
The Desk and the Riverbed — Sprinkle quickdust on a lectern, and it wakes as a Reckoning Desk. Lay the Codex on it, use it, and solve the lesson puzzle.
Where to get
Caches
Copyist's Lodge, the Inkpine Forest