Quarterdeck Sextant

Quarterdeck Sextant is an offline-first celestial-navigation workshop for coastal and offshore sailors who need to take a real sight and land a fix — not keep a passage diary. At the heart of the app is a brass drum sextant you actually operate. Drag the arc along the limb and the reflected sun walks down the horizon until its lower limb kisses the line. A knurled micrometer drum ticks out degrees and whole minutes, and a swing check tells you when the arc is tilted so you can rock it back to vertical. From there the sight tears off into a correction cascade: index error, dip, refraction, semi-diameter and parallax, each animated from Hs to Ho. Tap any chip to see its formula, then move the slider and watch the correction change in real time. Then reduce the sight to an intercept and drop it onto a Marcq St. Hilaire plotting sheet. Drag one to three lines of position along their azimuths, watch the cocked hat form, and get a rated fix precision in nautical miles with the weakest sight highlighted. A built-in low-precision solar ephemeris gives GHA, declination and equation of time for any date from 2020 to 2040, so the whole drill works in a cockpit with no signal and no paper tables. TRAINING THAT HAS TEETH • Timed Sight Drill Arena — shoot inside a target window against the clock. Scoring grades Good, Within 1 nm or Refraction slip, with streaks, per-skill badges and a personal-best table. • Twilight Star Plan — for your DR position and date, list the best two or three bodies with computed altitude and azimuth on a draggable horizon-to-zenith star dial, plus the civil and nautical twilight windows. • Noon Sight (LAN) Solver — find local apparent noon from DR longitude, watch the altitude peak, and get latitude with a sun held / still rising verdict so you learn to wait for the turn. • Compass Amplitude Lab — compute the sun's expected amplitude bearing at sunrise or sunset, compare it with the ship's compass, and read off a deviation value for the card. BUILT FOR THE COCKPIT • Fully offline — no network, no downloads, no almanac subscription. • Voyage Vault — save DR positions, routes and completed sights, reopen any sight sheet, and export a clean text or CSV sheet for a paper workbook. • Chart-Table Glance — a home-screen widget with today's sun GHA and declination, LAN time for your saved position, and the next twilight window. Made for ASA and US Sailing coastal-nav students, blue-water cruisers, maritime-academy cadets, tall-ship deckhands and offshore-racing crews who want honest numbers and graded practice. Fair warning: this is a training and practice tool. It is not a replacement for a certified sextant, a current nautical almanac or a formal navigation course, and it should never be the only means of fixing your position at sea.