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  1. #21
    Supporting Member Philip Davies's Avatar
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    The Greek, Olympian foot, (taken presumably from the stadium length, divided by 600) is cited as 1.01376 English feet. 6000 of these Olympian feet equals 6082.596 feet. The UK officially defined nautical mile is cited as 6082.56 feet. (Figures taken from Neal’s book)

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    Supporting Member Toolmaker51's Avatar
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    Quote Originally Posted by mklotz View Post
    Their odometer also had an ingenious mechanism for dropping pebbles into a container to register miles traveled...

    Ancient Rome: The Odometer Of Vitruv | History Of Physics
    That New World farmers reused as a seed planting device. That advantageous equal spacing eventually led to mechanization of harvest equipment.

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  3. #23
    Supporting Member mklotz's Avatar
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    Quote Originally Posted by Philip Davies View Post
    The Greek, Olympian foot, (taken presumably from the stadium length, divided by 600) is cited as 1.01376 English feet. 6000 of these Olympian feet equals 6082.596 feet. The UK officially defined nautical mile is cited as 6082.56 feet. (Figures taken from Neal’s book)
    This from Wikipedia...

    A nautical mile is a unit of length used in air, marine, and space navigation, and for the definition of territorial waters.[2][3] Historically, it was defined as the meridian arc length corresponding to one minute (1/60 of a degree) of latitude. Today the international nautical mile is defined as exactly 1,852 metres (6,076 ft; 1.151 mi).

    https://en.wikipedia.org/wiki/Nautical_mile
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    Philip Davies (Aug 11, 2022)

  5. #24
    Supporting Member Toolmaker51's Avatar
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    Quote Originally Posted by mklotz View Post
    This from Wikipedia...

    A nautical mile is a unit of length used in air, marine, and space navigation, and for the definition of territorial waters.[2][3] Historically, it was defined as the meridian arc length corresponding to one minute (1/60 of a degree) of latitude. Today the international nautical mile is defined as exactly 1,852 metres (6,076 ft; 1.151 mi).

    https://en.wikipedia.org/wiki/Nautical_mile
    Correct, mathematically. In practice, rounded to 6000 feet, enabling rapid mental calculations that work with 60 unit time, and divisible degree units of 60. When two 90,000 ton vessels may collide, a few seconds delay can be hazardous.
    It impressed me early on, having already begun machining, that navigation was so similar, just different words.
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    Supporting Member Saltfever's Avatar
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    In the mid 70s most all general aviation aircraft converted from mph to an air speed indicator calibrated in knots. Maule aircraft today are the only planes still using mph.

  7. #26
    Supporting Member Philip Davies's Avatar
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    Quote Originally Posted by Toolmaker51 View Post
    That New World farmers reused as a seed planting device. That advantageous equal spacing eventually led to mechanization of harvest equipment.
    We learned in school of Jethro Tullís seed drill, invented 1725, I read. This, it seems used a belt to convey grain from hopper to furrow. I am fortunate that the Museum of English Rural Life is close to my home, in Berkshire, where Tull was born. My late friend, Don Gill, a very skilled craftsman made a model, which is there.

  8. #27
    Supporting Member Philip Davies's Avatar
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    Quote Originally Posted by mklotz View Post
    This from Wikipedia...

    A nautical mile is a unit of length used in air, marine, and space navigation, and for the definition of territorial waters.[2][3] Historically, it was defined as the meridian arc length corresponding to one minute (1/60 of a degree) of latitude. Today the international nautical mile is defined as exactly 1,852 metres (6,076 ft; 1.151 mi).

    https://en.wikipedia.org/wiki/Nautical_mile
    The Dent dictionary of Measurement gives the following:
    UK nautical mile = 6082.66 feet (also called a “geographical mile”
    Admiralty nautical mile = 6080 feet (This is found on the Greenwich Observatory website)
    US nautical mile (international standard) = 6076.12 feet.
    I haven’t got the dictionary, but I view Neal’s figures with caution. There are frequent errors in English and occasional miscalculations, the latter of course are much harder to spot.
    The longer mile is apparently due to its being surveyed at a more northerly latitude.
    Last edited by Philip Davies; Aug 11, 2022 at 06:57 AM. Reason: Further explanation

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  10. #28
    Supporting Member mklotz's Avatar
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    Trying to tie any unit to earth geography is fraught with difficulties. The major problem is the earth's equatorial bulge. It gave the French difficulties when they tried to tie the meter to the equator-to-pole difference. (But remember, the exact value of the base of any measurement system is never important - good measurement systems are dependent on other characteristics.)

    The equatorial bulge affects satellites as well. The RAAN (Right Ascension of Ascending Node - the longitude at which the south to north path of the satellite crosses the equator - more here...

    https://en.wikipedia.org/wiki/Longit...ascending_node

    drifts westward due to the bulge. There is an equation that predicts the drift rate...

    https://en.wikipedia.org/wiki/Nodal_precession

    as a function of the earth's oblateness.

    I was once tasked to provide an improved gravity model that could be used to integrate the satellite's motion without using the drift rate equation. As it turns out, the oblate earth can be accurately modeled as a combination of a perfectly spherical mass with a torus around the equator to mimic the bulge. Then the net gravity acting on the satellite can be computed as a vector addition of the components arising from the sphere and the torus.

    Need I mention that computing the gravity field of a torus is a daunting mathematical exercise ? Using the equation is vastly easier.



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