Stratum Gauge Cards

Beneath the mirrored salt flats, north is a polite fiction. Expedition crews carry stratum gauge cards—palm-sized laminates of storm glass and charter vellum, etched with meridians ratified at the Glass Consensus Symposium. Each card is a portable slice of the sealed labs' argument with the world: if the salt's second sky agrees with the scored lines, the stratum is legible; if not, the card must be struck from the kit before anyone signs a depth log.

Construction

Card stock begins as off-cut storm glass—panes too thin for orreries but still harmonic. Mirror Spring chemists seal the glass between waxed vellum leaves impregnated with cartomantic ink. The ink does not draw maps; it remembers edges—fracture planes, vein mouths, places where starlight pools wrong. A fresh card smells of sealed laboratory and cold brine.

Field use

Surveyors lay a card flat on cleared salt and sight along its meridian while a companion holds the Violet Compass. When the needle drinks a constellation, the card's scored lines brighten or dull in sequence, revealing which buried layer answers the sky. Experienced readers, like Eris Valen, pair cards in offset pairs: one for the stratum you stand on, one for the stratum you are about to insult with a bore.

Limits and charter

Gauge cards are not weapons and not oracles. They fail in mirror-moth polish—air so reflective the card sees itself and lies. Syndicate assay will prosecute crews who sell stamped cards to ash peddlers; unstamped field laminates are expedition property and must be burned when the march ends. A card that fractures along a meridian during reading is treated as a salt signal in its own right: something under the flat wanted the line broken.