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Re: GPS VS SEXTANT / ASTROLABE

 

?*?How Accurate does a?*?
?*?Celestial Fix need to be?*?
This also includes GPS ?
Part 2 of 2 ?
Celestial navigation is used when you are far out at sea, when no other methods of position fixing are available.
?
If you are hundreds of miles from the nearest land, 10 miles of error in your position is not too significant.
?
Remember, in the middle of an ocean, you will be using a small scale chart. The chart probably covers most of the ocean.
?
Your position only needs to be accurate enough for you to make landfall in roughly the right place. After that, visual navigational techniques can take over.
Aka {LINE OF SIGHT} easly 10 miles or more.
Re: GPS VS SEXTANT / ASTROLABE

 

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Need a good watch if you want latitude and longitude.?

On 02-Mar-25 20:25, davesmith1800 wrote:

?? Sextant vs GPS ???
?
Part 1 of 2
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GPS is the most accurate around 40 inch or 1 meter.
?
The drawback list.? ?
?
  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.? ? ? ?
??????
?
The Sextant?
?
While the theoretical maximum accuracy of a celestial fix is 0.1 miles, in reality you will probably never achieve closer than 1 mile.
?
?
?
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.
?
In reality, however, it is almost impossible to actually achieve an accuracy of 0.1 minutes with a sextant.
?
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.
?
It is far more realistic to get an accuracy of 1 minute with a sextant in day-to-day conditions.
?
An accuracy of 1 minute with the sextant implies a final position fix accuracy of 1 mile.?
?
With some reading in WW2 the Navey found it 1? with a good operator most was under 5 miles .
?
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: .
?
  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
?
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?
?
Fortunately though, practise and precision can be used to reduce or eliminate most of these errors.
?
?
?
We can therefore say that an experienced navigator can realistically expect an accuracy of around 1 mile when completing a celestial position fix.?
?
?
?
Beginners, on the other hand, will be lucky to achieve an accuracy of 10 miles the majority of the time.
?
?
?
Dave?
GPS VS SEXTANT / ASTROLABE

 
Edited

?? Sextant vs GPS ???
?
Part 1 of 2
GPS is the most accurate around 40 inch or 1 meter.
?
The drawback list.? ?
?
  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.? ? ? ?
??????
?
The Sextant?
?
While the theoretical maximum accuracy of a celestial fix is 0.1 miles, in reality you will probably never achieve closer than 1 mile.
?
?
?
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.
?
In reality, however, it is almost impossible to actually achieve an accuracy of 0.1 minutes with a sextant.
?
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.
?
It is far more realistic to get an accuracy of 1 minute with a sextant in day-to-day conditions.
?
An accuracy of 1 minute with the sextant implies a final position fix accuracy of 1 mile.?
?
With some reading in WW2 the Navey found it 1? with a good operator most was under 5 miles .
?
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: .
?
  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
?
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?
?
Fortunately though, practise and precision can be used to reduce or eliminate most of these errors.
?
We can therefore say that an experienced navigator can realistically expect an accuracy of around 1 mile when completing a celestial position fix.?
?
Beginners, on the other hand, will be lucky to achieve an accuracy of 10 miles the majority of the time.
?
Dave?
?
[img]https://th.bing.com/th/id/OIP._r0SgDl4wmCPBVt4pQVWSAHaFj?w=166&h=124&c=7&r=0&o=5&dpr=2&pid=1.7&PC=EMMX01[/img]?
Re: On the Funny Side

 

Re: On the Funny Side

 

Thus what need next Halloween?
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Re: On the Funny Side

 

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Re: On the Funny Side

 

Found the bug is a mouse?
Now need a mouse trap to fix my wires
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ROUGHNESS/FINISHED comparator

 

Most production machine Shop will have this for both quoting and doing.
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This also used in design and? engineering so can receive the finished whan on part. This finished can change the cost of making the parts.
This where I used is beside the drafting board.? First start with black plastic and later purchase the chrome one for better view.??
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So if see this on drawing you know more about why.?
?
Dave

Re: Hardness tesrters

 

Chart on different hard scales?
Re: Hardness tesrters

 

Here what put book in 2015.
It from the hardness tester I have from 1970’s?
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I wrote book before I had 106 Chemotherapy treatments?
Re: Measure

 

I like your post after reading I change this ON THE FUNNY SIDE and forgot this good one if want please repost to the ON THE FUNNY SIDE.
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PLEASE POST MORE FUNNYS
Dave?
Hardness tesrters

 
Edited

Here pass from 1970’s patten too.
A ball drop
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Today's hardness tester?
A ball drop notice the size?
?
? ?
[COLOR="#800000"][b] [CENTER]???? ? ??? [/CENTER].? ?[/B][/COLOR]?
This side I use on I purchased in the mid 1970’s I have posted this side only? since 1999. one first got the Kro printer for drafting in 1979 I hardness for ?" plate since most die work using ?" stickand only side showed?
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============= other brand =============
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This today's $279.00 you buy new 2025
?
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=====The day I purchasedin mid 1970’s====
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This is how came brand new in mid 1970’s.?
The above is side post since 1999 on groups.
They used Millimeter in the mid 1970’s?
?
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WHAT I SAY IS Hight lite to see answer?
?COPY CAT?
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WHAT DO YOU THINK??
?
Re: On the Funny Side

 

Re: On the Funny Side

 

Lucky dog
  1. Warm teepee?
  2. Scrape?
  3. Only do guard duty while sleeping?
  4. Health care?
  5. Bed?
?
Dave?
?
Re: On the Funny Side

 

?
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Re: Magnetic North vs True North

 

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It's hard to find current data, but the movement of the poles has been speeding up.? You can see it some from 1980 to 2015 but it's moved quite a bit in 10 years.? The south pole is headed for the Indian Ocean.? Also the strength has been dropping which can cause instability in a compass.

Getting current data is again not easy.? Some sources have the rate of decrease accelerating past this chart.




On 28-Feb-25 7:49, davesmith1800 wrote:

?
Here little data on magnetic north vs true north.?
?
Re: Magnetic North vs True North

 
Edited

Here a web site show the magnetic north vs true north.? The compass part may work if you have the magnetic senor?
?
?
?
Dave?
Magnetic North vs True North

 

?
Here little data on magnetic north vs true north.?
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Re: Sextant design & build

 

Here chart on miles vs degrees?
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Re: Sextant design & build

 

Here is small version? 4" x 4" [100mm x 100mm] if note the find adj? had removed.
It could be more work to get down to 3" x 3"?
?
Dave?
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1A_ SEXTANTSmaller ver.pdf
1A_ SEXTANTSmaller ver.pdf

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