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[airhead969]

The smallest possible resolution of GPS in the horizontal is 10mm (6-7 digits) with local differential corrections.

In general, 4-5 digits is the precision to expect.

[jstanley → airhead969]

Hm, then I think my calculation that the 14th digit is worth 0.15mm must be wildly incorrect.

For a 40km earth circumference, I worked out 10^-14 * 360 * 4*10^7 = 0.00014 metres.

[schoen → jstanley]

I think you want to divide by 360 instead of multiplying by 360 - when you divide by 360, you should get the linear distance represented by one degree of latitude or longitude.