?? Sextant vs GPS ???

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Part 1 of 2

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GPS is the most accurate around 40 inch or 1 meter.

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The drawback list.? ?

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1. Satellite ? and other countries take out
2. Satellite and space debre
3. Sun spots?
4. Thunder ?
5. Power aka battery dead?
6. About anything effecting electronics.? ? ? ?

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The Sextant?

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While the theoretical maximum accuracy of a celestial fix is 0.1 miles, in reality you will probably never achieve closer than 1 mile.

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How Accurate is a Celestial Position Fix?

The theoretical accuracy of a celestial position fix is based on the accuracy of a sextant. Most sextants let you measure angles to within 0.1 minutes of a degree. 0.1 minutes {6 seconds 0.12 miles 600 feet at equator } on the altitude of a celestial body translates to 0.1 nautical miles on the surface of the earth.

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In reality, however, it is almost impossible to actually achieve an accuracy of 0.1 minutes with a sextant.

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You are taking your measurements from a moving boat, which is floating on a moving ocean. The horizon needs to be clear, and the celestial body needs to be a perfect, bright speck.

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It is far more realistic to get an accuracy of 1 minute with a sextant in day-to-day conditions.

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An accuracy of 1 minute with the sextant implies a final position fix accuracy of 1 mile.?

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With some reading in WW2 the Navey found it 1? with a good operator most was under 5 miles .

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Of course, getting that sort of accuracy relies on minimising every other source of error. Unfortunately, in celestial navigation, there are plenty of potential sources of error: .

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1. Errors reading the measurement from the sextant
2. Errors identifying a celestial body
3. Potential inaccuracies in your chronometer
4. Errors in identifying prevailing atmospheric conditions
5. Errors in your calculations
6. Rounding errors
7. Errors plotting the final fix
8. operator holding the sextant

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On plus side is?

1. no power need?
2. No satellites?
3. Works with Sun spots
4. Works when electronics does not?
5. No power need or batteries?

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Fortunately though, practise and precision can be used to reduce or eliminate most of these errors.

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We can therefore say that an experienced navigator can realistically expect an accuracy of around 1 mile when completing a celestial position fix.?

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Beginners, on the other hand, will be lucky to achieve an accuracy of 10 miles the majority of the time.

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Dave?