Monday, January 14, 2019

Educate Me About Compass Types

 Originally, I glued a very tiny compass on the base plate.  It took a while for me to figure out that I needed the polar axis pointing to 349 degrees; true north, is 11 degrees west of magnetic north.  The compass is tiny, and hard to read unless I get on my knees.  I use the Compass app on my once and future cellphone to get the big telescope pointing to true north, but it is not as easy as I would like. 

The Compass Store has more types of compass than I knew existed; one with glowing pointer, 8-12" diameter, and a flat bottom would be perfect.  Baseplate, Sighting, Orienteering...  what am I looking for?


  1. you can get one designed for Navigation that has iron masses to allow for the offset from true north.

  2. Offset not important. Just need to be able to read when the arrow is pointing at 349 degrees.

  3. Silva Ranger 15 style. Silva, Brunton, Suunto, all good brands. Or one with a similar rectangular baseplate, the sighting feature isn't essential.....

    Then, don't worry about seeing it in the dark: Find a distant object on the correct bearing you want, and line your scope up to that.

    The 15 style can also usually have an offset feature for declination: Set it once and forget it (until you move).

  4. I'm guessing, but a boat/ship's compass would probably be the biggest class you would be likely to find. There are electronic versions that use gyros (also used in aircraft), but you are already heading into high dollar territory. Ideally, you want to find a compass off an old yacht that is being broken up for scrap. Might be referred to as a binnacle?

  5. One problem you may run into (not related to the specific compass type, necessarily): if you're mounting it in or around a mass of steel, you may find problems with magnetic interference.

    We were always taught to be careful of our weapon and other densely metallic gear when using our lensatic compasses for land navigation, for this reason. Depends on how precise you need to be as to how much of a problem this could be, I imagine.

    In any event, I've always found the standard military-style lensatic compasses to be the most reliable and durable around, FWIW.

  6. Any baseplate compass ought to be suitable for that then. You won't need a $50 one for navigation with a separate needle to point at 349 degrees. $10 should get you a very nice one.

  7. Can Dead Men Vote Twice At Elections?
    C = compass reading
    D = deviation (compass error)
    M = C + D (see below) yields magnetic
    V = vairence Local variance is on your charts*
    T = M + V yields true heading
    A E = add East. If the deviation or variance is “east” add it. Otherwise if “west” subtract.

    * I have read recently that variance is moving at an ahistorical pace. Variance measures the distance between the true north or the earth’s axis and the magnetic north as seen at your location.

    As to your original question, there are two types of compass; magnetic and gyroscopic. The latter are big bucks.

  8. Forgot to mention these bad boys.

    Put one sensor at each end of your scope and you’re golden. Some adult assembly required. A new product line for Scope Roller?

  9. Forgot the reverse: True Virgins Make Dull Companions At Weddings.
    The usage is left as an exercise for the interested student.

  10. I am having trouble visualizing how you are trying to align your telescope. To me you need to plan in the summer to have a compass face painted on the site where you usually set-up the telescope. Then when you do bring the telescope out you rest it on the ground mark and then adjust until it is pointing 349 degrees.

  11. Phosphorescent paint line already painted north, but not highly visible in dark, especially in snow. The only object on that bearing is the North Star, not visible in early twilight. There is no steel in any part of the telescope near the base: birch, Pyrex, aluminum.

  12. How about an aiming stake, laid out due north? You could use a T-post or something similar...if you want to get fancy, a red solar powered LED bulb will allow sighting the scope on it without disturbing night vision too much..

  13. I think Fidel's idea would work for you. You would also need to put the telescope in exactly the same spot so you would get consistent alignment.

  14. In a sense, I already having an aiming stake: Polaris, but is not visible until it is quite dark; hence the compass. I am also worrying about my aortic valve beginning to fail; this all may be moot in a couple of years.

  15. You need an aiming point you can see, right?

    Much like being able to lay mortars.

    Perhaps putting a nail in your nice smooth asphalt where the scope will go, and then lay out a string on the bearing 349 degrees magnetic - you would need a compass with no more than 2-degree markings. Of course, minimize metal near you while doing this.

    Put the aiming stake out at the end of the string, on the bearing. Spray paint the top of it white or glow in the dark, or put a reflective lane marker on it.

    When you set up the scope, it goes over your base point, and lines up with your aiming stake. Et voila! It is oriented towards true north.

    As far as your heart valve and have been on airplanes with very dry air lately...perhaps that has something to do with coughing?

    Best wishes,

  16. Assuming that magnetic interference isn't a problem (a *big* sasumption) - how about clamping your cell phone to it when you need to align it. The cell phone has good magnetic sensors, and you can easily find apps that will point north - and reading in the dark is trivial.

  17. Fidel: Good idea about how to get a long line to true north. Perhaps the airplane dry air is aggravating things.