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Thread: Compass

  1. #1
    Senior Member sibyrnes's Avatar
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    Compass

    Have any of you tried this:

    Marlin's Quest Compass in Talon Motorcycle Handlebar Mount - Satellite Driven

    If so, what mounting method did you use. Any luck with magnetic compasses?

  2. #2
    Super Moderator Purple's Avatar
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    So - you get a powered compass, with a GPS, that points North – for 120 bucks

    No electricity – no pointy

    Last year, I got four “traditional” compasses from China – for about 3 quid, delivered – granted, you have to be careful to get an accurate North, but it’s still $120 cheaper …..
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    Senior Member Fred's Avatar
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    Does the Marlin display magnetic or true north? Being satellite based it is likely displays "true" north but knowledge of magnetic north is helpful because some data bases like aeronautical and marine charts indicate magnetic bearings.declination 1.png
    Conventional compass uses need to compensate for declination depending on where you are on the planetdeclination.jpg

    Don't forget that with the traveling magnetic pole declination changes yearly. Does the Marlin compensate for this too if one wishes to know current magnetic bearings? declination 2.jpg
    Last edited by Fred; 05-11-2018 at 09:18 AM.
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    Senior Member mrlmd's Avatar
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    "Declination" refers to altitude above the horizon, ie., the angle north or south of the equator.
    The word you are looking for to describe the east or west magnetic pointing of the compass relative to True North (geometric north) is "Variation".
    The amount Magnetic North differs from True North is the Variation and it depends where on the planet you are and it may change year to year based on the magnetic north pole changing its position slightly year to year.
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    Senior Member Trail Woman's Avatar
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    I'd prefer the old school compass myself. Much like the TW I prefer simpler more independent technology.

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    Senior Member Fred's Avatar
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    Sorry mrlmd, we must come from different disciplines for I have been taught, have taught, and regularly compensate for what is overwhelmingly referred to as magnetic declination for over the last 40 years in the various surveying and engineering activities in which I have been involved . Always hated the math entailed in determining local declination via late night observations of the North Star Polaris. Never tried it with the Southern Cross but that would really hurt my brain.
    While sometimes referred to as "variation" by geophysicists and others the term "declination" is the typical term I encounter and use used in the data bases I have dealt with from USGS, NOAA, property records, legal descriptions, court documents, county records, etc.
    Both terms are valid expressions for the permutations in the earth's magnetic field which very over time and location.
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    Senior Member admiral's Avatar
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    Quote Originally Posted by Fred View Post
    Sorry mrlmd, we must come from different disciplines for I have been taught, have taught, and regularly compensate for what is overwhelmingly referred to as magnetic declination for over the last 40 years in the various surveying and engineering activities in which I have been involved . Always hated the math entailed in determining local declination via late night observations of the North Star Polaris. Never tried it with the Southern Cross but that would really hurt my brain.
    While sometimes referred to as "variation" by geophysicists and others the term "declination" is the typical term I encounter and use used in the data bases I have dealt with from USGS, NOAA, property records, legal descriptions, court documents, county records, etc.
    Both terms are valid expressions for the permutations in the earth's magnetic field which very over time and location.
    In 27 years in the military I've always been taught the term was True North to Magnetic North Declination as well. Heck, even the Forest Service Maps call it this (look at bottom of Map). Maybe there are other terms which mean the same thing.
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    Super Moderator Purple's Avatar
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    Compass bearing = true bearing +/- magnetic variation/declination +/- compass deviation

    Not all compasses are the same (just to add to the confusion)

    “North” is best described as “probably somewhere over there” ……
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  10. #9
    Senior Member admiral's Avatar
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    Quote Originally Posted by Purple View Post
    “North” is best described as “probably somewhere over there” ……


    Love it, use it. Usually, by waving my hand and arm in a back and forth manner giving plenty of error on either side of the "perceived northerly direction". Sometimes I can see the sun and that helps me point more north than I was originally thinking.
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    Senior Member mrlmd's Avatar
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    I don't want to start a war on here, but every navigational or nautical reference as well as every published government nautical chart has a compass rose with VARIATION on it. All the government publications for planetary or star sightings used for celestial navigation or observation and location, ie., with a sextant or any other instrument, refer to the star's height above the horizon as its' DECLINATION, also called altitude.
    Look up the definition of these words in a dictionary or do a Google search if you don't believe me.
    I find it hard to believe that there would be interchangeability between these two words in trying to describe such a precise mathematical measurement. It would make it very confusing to discuss any of this as they have 2 different meanings in 2 different disciplines. That's like how the NYPD can't communicate with the NYFD because they are on 2 different radio frequencies and can't talk to each other.

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