Sight through Compass / Clinometer by Suunto

11:16 p.m. on October 20, 2009 (EDT)
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3,956 forum posts

I have a chance to buy a friends sight through Suunto Tandem.

Does anyone have any experience with one?

Are they any more accurate (for back packing) than a standard compass with clinometer? I often take readings from peak to peak, or peak to Polaris, etc, just for fun & to practice. Would the Tandem be a help, or just dead weight?

I would welcome any substantial advise.

1:25 p.m. on October 22, 2009 (EDT)
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5,917 forum posts

The Suunto Tandem and the similar (but superior, in my opinion) Silva (sold in North America as the Brunton SUM Survey Master) are way overkill for your purposes. Unless you want to get survey accuracy, at which point you really should get a transit.

Suunto Tandem

Silva/Brunton Survey Master

Since they are sight-through instruments, they are more precise than most handheld compasses, and about the same accuracy as the Brunton Pocket Transit, about 0.5 deg if you are well-practised (remember that precision and accuracy are different things). The usual handheld compass is calibrated at 2 deg intervals, and can be read consistently to about 1 deg if you are well-practised, even the fancier mirror and lensatic compasses. The clinometers in the "Ranger" compass series for both Suunto and Silva/Brunton are marked at 2 deg intervals as well, though in actual use you will do well to get 4 deg accuracy consistently (for many reasons, including practice) The vast majority of users do well to get 2 deg accuracy with any consistency. I have the Silva and find it useful when doing my rough survey work for our timber management to satisfy CalFire regulations or when setting orienteering courses (though I haven't done that in several years).

Here is a test for you to check your skills (and good practice for honing your skills) - pick a location with two easily sighted and well-defined points at least 200 meters/yards apart. You want something you can readily see, but of small size. Take front and back sights from one to the other several times (measure the bearing from A to B, then go to B and get the bearing from B to A). The reason for the repetition is to check on your consistency. The front and back sights should be 180 deg apart. Do this on several days separated by a week or more (to reduce the memory effect of forcing the readings to match). If you can consistently get your readings to match within 1 deg (interpolate between the markings on the compass), then you may be ready for the Tandem or Survey Master. But remember that you will only step up to a 0.5 deg accuracy level.

6:18 p.m. on October 22, 2009 (EDT)
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3,956 forum posts

Thanks Bill,

I would have to say that I am not able to use my instruments to their full capability or accuracy. I am often off by 3 to 5 degrees in the back country. Sometimes when I emerge from the bush onto a trail I will be a good distance from the spot I had marked on the map. Obviously this is mostly user error, sometimes I make excuses, but it's always my fault, none the less.

I practice often, when at work I can sight distant objects and try to at least 3 or 4 times a week, with a map. Honestly, I'm probably in the 2 - 3 degree range most times.

With the clinometer I'm not sure how far off I am, I rarely have a real need to know slope angle, but I sometimes take reading for fun.

I know I am off simply because I take readings at standing eye level to top of slope, so I am instantly off by the amount my body height affects the reading. So far I've just been concerned with holding and reading the clinometer correctly from that position.

I will practice with the method you described Bill, repetition is not something I have concentrated on. You raise a good point.

I am probably going to get the Tandem while I can get a bargain on it, but I understand it is overkill for most of what I do. It will probably end up being a toy.

Thanks for the advise.

11:28 p.m. on November 10, 2009 (EST)
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9 forum posts

There is probably very little difference in error between even the least expensive compasses and the more expensive ones - most of it is definitely operator error. It can be very difficult to follow a perfectly straight line through rough bush, especially where there are a lot of hills.

March 28, 2017
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