Dead Reckoning Error Estimator
Estimates position error accumulation over a multi-leg route with no GPS — for when electronics fail.
Inputs (per leg, average)
Result
A natural placement between the calculator and the explanation.
What this solves — and what it doesn't
When your GPS dies, you fall back on dead reckoning: tracking pace count + compass bearing + time. Each leg has small errors that accumulate. Cross-track error from a slightly-wrong bearing grows with the square root of legs (random walk); along-track error from pace mis-estimation grows linearly. Total position uncertainty is the root-sum-square of both.
How to read the result
The result is a ‘±X meters’ radius around your estimated position. The 1-sigma number means you’re roughly 68% likely to be inside that circle; double it for 95%.
On a 10 km day with 5 legs, expect ~200 m of uncertainty — about 2 contour lines on a topo map. Big enough to miss a small trail junction.
Limitations
- Assumes errors are unbiased. Systematic slip (e.g., drift in your pace count) can be much worse.
- Doesn’t model the value of terrain association (rivers, ridges) which drastically reduces error.
- Compass accuracy is your constant; declination error is folded in.
Frequently asked questions
Should I use time or paces?
Both. Pace counts catch terrain changes; time catches distance on flat ground.
How do I reduce error?
Shorter legs, frequent terrain association (rivers, ridges), and rigorous declination setting.
What about map-and-compass alone?
Classic compass. Resection from two visible features can fix your position to within 50 m.