Master Clock

Master Clock is a GPS-disciplined navigation instrument for iPhone,

designed for anyone who needs accurate time and position in the

field — at sea, in the mountains, or anywhere off the beaten track.

ACCURATE TIME

The clock is disciplined by GPS satellite time and cross-checked

against NTP network time, giving you UTC to within a fraction of a

second. The analogue clock face runs at up to 120 Hz for perfectly

smooth second-hand motion.

NAVIGATION INSTRUMENTS

Choose between a full analogue dashboard and a digital readout:

• Compass — true heading from the magnetometer, or course over

ground from GPS. Smooth, high-refresh needle motion.

• Speedometer — speed over ground in knots, km/h, mph or m/s,

with a green band marking your planned speed range.

• Position — latitude and longitude in degrees/minutes or decimal,

with altitude and GPS accuracy.

• Sun times — sunrise and sunset for your current position,

calculated offline from your coordinates.

POSITION LOGGING

Start a logging session and Master Clock records your position,

speed, course and distance made good at your chosen interval.

Sessions run in the background with the screen off, confirmed by

an audio beep. Export your log as a CSV file for analysis,

passage review, or field records.

SPEED ALERTS

Set a planned speed range and Master Clock will alert you — with

a banner and an audio tone — when your speed falls outside it.

Useful for sail trim, tidal planning, or pacing on a long passage.

LIVE ACTIVITY

A lock-screen Live Activity shows your speed, course and position

at a glance while a logging session is active.

NIGHT MODE

A red-on-black night mode preserves your dark adaptation at sea

or under a night sky. Auto mode switches at local sunrise and

sunset for your position.

GPS INTEGRITY MONITORING

Master Clock watches for signs of GPS interference: NTP time

drift, location freeze, and physically impossible position jumps.

It distinguishes the common benign cases — indoors, tunnels,

re-acquisition after a ridge — from genuine anomalies that warrant

a position cross-check.

PRIVACY

Your location data never leaves your device. Log files are

excluded from iCloud backup. No account, no subscription,

no analytics.