Compass Turn Error Calculator (UNOS / Lead-Lag)
Northerly turning error quantified: the lead or lag for your latitude and target heading — undershoot north, overshoot south, by this many degrees.
The whiskey compass's card is a pendulum in a magnetic field that dips toward the earth at your latitude — turns through north show it lagging, through south leading. UNOS is the partial-panel survival rule; the magnitude is roughly your latitude.
Formula
⚠️ For flight planning and education only — verify with official sources and certified equipment. Not for primary navigation.
Northerly turning error quantified: the lead or lag for your latitude and target heading — undershoot north, overshoot south, by this many degrees.
About Compass Turn Error Calculator (UNOS / Lead-Lag)
Lose the vacuum pump and the magnetic compass becomes primary — a gimballed pendulum that lies during every turn in a latitude-sized way. This calculator quantifies the northerly turning error for your rollout heading and latitude: which way it lies (UNOS — undershoot rolling out north, overshoot south), by how many degrees, and the indicated heading at which to begin the rollout. Partial-panel training's vaguest rule of thumb, given numbers.
How to use Compass Turn Error Calculator (UNOS / Lead-Lag)
- 1Enter — sensible defaults are pre-filled so you see a worked result immediately.
- 2Read the live results: .
- 3Check the "With your numbers" line to see the formula dip error ≈ latitude × |cos(heading)|; UNOS: Undershoot North, Overshoot South substituted step by step.
- 4Adjust inputs (or flip the unit toggle) until the scenario matches yours, then copy or share the result.
Why use Compass Turn Error Calculator (UNOS / Lead-Lag)?
- ✓Instant, free and private — every calculation runs in your browser, nothing is uploaded
- ✓Built on the published formula dip error ≈ latitude × |cos(heading)|; UNOS: Undershoot North, Overshoot South with sources cited on the page
- ✓The whiskey compass's card is a pendulum in a magnetic field that dips toward the earth at your latitude — turns through north show it lagging, through south leading. UNOS is the partial-panel survival rule; the magnitude is roughly your latitude.
- ✓Switch units, tweak any input and watch every result update live
Frequently asked questions
What physically causes northerly turning error?+
Magnetic dip: Earth's field lines plunge toward the surface at an angle roughly equal to your latitude, and the compass card's pendulous weight responds to the vertical component during banked flight. Turning through north, the dip-induced torque swings the card opposite the turn (it lags); through south, with the turn (it leads). On east/west the geometry cancels.
How do I apply UNOS in an actual partial-panel turn?+
Decide the rollout heading, apply this tool's lead/lag (≈ your latitude when rolling out near north or south, fading to zero near east/west), and begin the rollout when the compass shows the adjusted value — plus the usual half-bank-angle allowance. Or sidestep the lying card entirely with timed turns: our standard-rate timing tool computes the seconds.
Does the error direction flip in the southern hemisphere?+
Yes — dip points up-out of the ground there, reversing the torque: SOUN (overshoot north, undershoot south) is the southern-hemisphere rule. Equatorial flying enjoys near-zero dip and an honest compass in turns; polar flying suffers so much dip the magnetic compass becomes unusable, which is why polar navigation went gyro/true decades ago.
What about ANDS — the acceleration errors?+
The same pendulous card also lies under acceleration on east/west headings: Accelerate-North, Decelerate-South in the northern hemisphere. Speed changes during compass turns thus compound the turning error — the discipline is constant airspeed during partial-panel turns, changing one variable at a time. Glass magnetometers (fixed sensors, no pendulum) sidestep both error families entirely.
Related Field tools
Sunrise & Sunset Calculator
Exact rise, set, solar noon and day length for any place and date — the NOAA solar equations with the refraction fine print included.
● LiveGolden Hour & Blue Hour Calculator
Tonight's golden hour and blue hour, computed from sun elevation — the photographer's light windows with the angles that define them.
● LiveDay Length Calculator
Hours of daylight for any date and latitude, how fast it's changing, and the swing between your solstices.
● Live