Magnetic dip varies from 0° at the equator to 90° at the magnetic north pole.
In order to counter magnetic dip most sensitive compass needles have a counter weight on the south end of the needle (in the Northern Hemisphere) which consists of a little bit of copper wire which can be adjusted for changes in latitude.
My Transit has the counter weight and I noticed when the needle is free and the instrument level the south end is a little higher than the north end but it still swings free. This makes sense because the Instrument originally came from Arizona (it has a Servco sticker on the box with a Phoenix address). My father told me he acquired the instrument from a Party Chief in Bakersfield in the early 1970s. I have the declination set for the current value reported for my zip code.
The difference in magnetic bearings to three objects (two angles) closely matches the angles measured on the vernier (within half a degree). I don't know if the needle should be perfectly level or just close. In order to adjust it I would have to figure out how to get the glass off then it probably wouldn't take much to adjust it (maybe just breathe on it).
If the clouds don't obscure Polaris this afternoon then I will get an observation to it this afternoon backsighting a steel gate post several hundred feet east of my house. I chose the location on my front lawn which should be as free of local attraction as possible (power lines in the back and parked vehicles in the front).
I was wondering about my Silva Ranger (I have an older one) but I think those are generally set up for the Continental US. It is marked to 2° and can be read to 1°. If I am careful I get very good directions from it assuming there is no local attraction. It seems to be more sensitive to nearby vehicles than my transit. At one spot the Transit showed about 1.5° local variation while the Silva showed more like 5 to 6° local variation (nearby parked vehicles).
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In aviation magnetic dip is an entirely different problem. On a north or south magnetic heading when the wings are banked the whiskey compass will initially show a 30° swing opposite the direction of the turn. On an east or west heading the magnetic dip is zero degrees. So making compass turns is a little tricky because the error changes with heading. Most airplanes have a gyroscopic heading indicator which is an instrument that is set to the whiskey compass either in level flight or on the ground then the heading indicator always indicates the correct magnetic heading except that it precesses a little over time so has to be reset occasionally. In airplanes we aren't splitting hairs, the compasses are marked to the nearest 5°. Then there is deviation which is the attraction of the compass to the metal parts of the airplane. It is somewhat corrected by magnets inside the compass body but never completely and it varies with heading.
Dave
I would think that a "minor" tilt of the magnetic needle wouldn't be any problem as long as the point of the spindle is in good shape.
As an aside. I have heard, and read, of pilots "boxing the compass". What does that entail and how is it done?
Andy
Dave
I think that is a nautical thing.
I never used points of the compass. Everything was in azimuth degrees measured from magnetic north.
Instructions from Air Traffic Control are known as "vectors." For example, Cessna Two Three Zero One Romeo turn right heading Two Four Zero which means to turn to a magnetic heading of 240 degrees.
Dave
A minor dip is not a problem. It is an easy fix to "balance" the needle with a slide of the ballast. It is also a necessary adjustment when you travel up and down across the latitudes.
An well magnetized and adjusted needle will not remain stationary and can be described as lively. It will actually "jump" as it reacts to the flux of earth's magnetic field.
Dave
I thought this was a ground up magnet, in somebody's can of skoal!
My bad.
N
> In order to counter magnetic dip most sensitive compass needles have a counter weight on the south end of the needle (in the Northern Hemisphere) which consists of a little bit of copper wire which can be adjusted for changes in latitude.
>
> My Transit has the counter weight and I noticed when the needle is free and the instrument level the south end is a little higher than the north end but it still swings free. [...]
>
> I don't know if the needle should be perfectly level or just close.
The standard, I believe, is to have the needle balanced so that the North end can be read most easily. That's what counts.
I set up on a 12" spike in my front lawn and sighted a natural target about 740' to the east.
The mean of 3 sets to Polaris yields N 89°40'53" E.
I observe a hair over N 89° E (about 5') with the Transit compass.
The Silva Ranger: I got about N 87-1/2° E.
The corner of my house 24' northerly:
Polaris N 07°06' W (a single angle from the natural above).
Transit N 08-1/4° W.
Did not sight it with the Silva Ranger.
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It is difficult to read the north end of the transit compass due to the stuff in the way but it would probably be better if I adjusted the counter weight back a slight amount.
> It is difficult to read the north end of the transit compass due to the stuff in the way but it would probably be better if I adjusted the counter weight back a slight amount.
It shouldn't be that difficult to do. The weights on the needles were intended to be slid around a bit.
See: "Directions for Magnetic Measurements" Third (1930) edition - corrected 1947, Daniel L. Hazard, Serial No. 166, Coast & Geodetic Survey, GPO, 1947, 129 pp.
Dave
Well, at first when I read the subject, I thought it was probably a post directed at me.....then I realized that I'm not all that "magnetic".
I checked my Dietzgen and the ring around the compass glass unscrews.
My Davis, Foote, and Kelly Fifth Edition, 1966, has a detailed diagram of a "typical" engineer's transit that matches mine pretty well. Chapter 13 gives instructions for all the adjustments (with confirming tests) that can be done outside the factory.
please post a photo
Please post a photo of this type of instruments
thanks for your help
please post a photo
This ebay listing has some pictures of the 6100. My 6300 doesn't look much different. I'll be surprised if they get their asking price - $900 is about twice what I'd expect.
http://www.ebay.com/itm/270991080816
And here's somebody's youtube