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Reply to "Elevations from various sources"

That's the report that Pete provided a link to earlier in the thread.

Those 9000+ points had a median separation of 2200 meters, and the standard deviation of their relative elevation error was 2.08 meters, so the 95% confidence level (approximately 2 standard deviations) is 4.16 meters.

The standard deviation of the elevation error (not the relative error) for the points is 2.44 meters. If we subtract a distribution with a standard deviation of 2.44 from another distribution with the same standard deviation, the result is a distribution with a standard deviation of 3.42. This is the standard deviation of pairs of points that are essentially infinitely far apart.

So in summary we have

Distance apart: 95% confidence level
0 meters: 0 meters
2200 meters: 4.16 meters
very far apart: 6.84 meters

In addition, you would expect the standard deviation of the error at 90 meters separation to follow a similar pattern as the mean error at 90 meters separation. This would give us an additional point of

Distance apart: 95% confidence level
0 meters: 0 meters
90 meters: 1.98 meters
2200 meters: 4.16 meters
very far apart: 6.84 meters

A function of the form

error = 6.84 X exp(c1 x separation ^ c2)

can be fit to this data.

The result can be used to make an estimate of the accuracy of the drop value for different course lengths as shown below.

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