Transit Compass

[Wayland]

Having just checked the long clinometer level against my builders level, there seems to be about a quarter of a degree difference.

I am inclined to trust the clinometer as it's level seems the more sensitive of the two.

Either way, ¼° (or 15' or arc) is probably more accurate than I could reasonably expect to get from a hand held sighting with clinometer anyway.

Obviously this cannot compare with the accuracy of a good sextant and could amount to as much as 15 nautical miles inaccuracy in position, but as I am unlikely to be carrying a sextant with me in most instances it certainly out performs a Kamal or similar makeshift methods.

For map work it suffers the obvious disadvantage of not having a built in protractor like a baseplate compass. This can easily be remedied buy using a separate one or even carrying a small baseplate compass as well, giving a back up too.

I should mention the case, it is reasonably sturdy and lined with thin closed cell foam. It is fit for purpose if a little ugly. I can see myself making a better one at some point but for now this will suffice.

The Brunton instructions suggest putting the top of the compass away from the press stud to protect the mirror from breakage. I am going to assume the same precaution is wise with this one too.

I will take it up my local fell this afternoon and give you some further impressions then.

 

[pteron]

Thanks for the write up Wayland.

So you are happy with it for the money?

 

[Wayland]

Just got back from the fells.

I took some map bearings before I went, for features I knew I could see up there, A mill chimney at about 3km and a church tower at just over 2km. I had figures from a car park and a trig point a click apart so the distances vary slightly.

The car park bearings checked out exactly and to -½°. The trig point bearings were also exact for the chimney and -½° for the church tower. Closer examination of the 25K map show that the building has been overwritten with the church tower symbol. I used the centre of the square as my point but I think that may be incorrect on the ground. A small church length at 2 clicks is not too bad though I guess.

On the fell I also took some bearings from the same features, and a new one too, at a point in between my two reference points and used these to get a fix on my position.

The lines crossed within 2mm on the map, again my wandering church being the furthest out, and the other two being spot on a fence line almost exactly where I was standing.

This is by far the most accurate results I have achieved from such a test. I have never been given cause to actually doubt the accuracy of an OS map before.

All these bearings were taken using the long sights with the compass resting on solid points. In two cases dry stone walls and a wooden gate post for the position fix.

Hand held bearings were made a little more difficult by the hunting of the needle, but not impossible. For hand held readings you can brace the compass at your waist and sight using the mirror as shown in the Brunton Instruction Manual.

Something I should have mentioned is that the instructions supplied with the compass are in Chinese, so unless that isn't a problem you will want to check out the Brunton instructions anyway. The compass is more or less the same functionally.


Pros:

Capable of taking very accurate bearings with a little care.

Capable of measuring vertical angles.

Allows magnetic declination (or variation) to be set on the dial.

Solidly built.

Not liquid filled meaning no more annoying air bubbles.

Inexpensive for an instrument of this quality.

Cons:

No built in protractor.

Requires a bit more knowledge and skill to use to it's full potential.

Not liquid filled requiring more time for the needle to settle.

Fairly heavy and a bit bulky.


So, in conclusion: Is it good value for money? Well for me it ticks all the right boxes. Most of the "Cons" listed above do not bother me at all, although I do wonder about the damped version which seems to be about £40 on ebay. If I'd seen that before ordering I may have gone for it but I'm not too worried now.

On the whole I like this a lot.

It's not a fast compass to use and it's not something you would tramp along with in your hand, so it wouldn't suit orienteering for example. In practice I only tend to use a compass when I want to check something, and accuracy is what really counts then.

Yes, I think this is very good value for £26.

 

[Tiley]

Great review. I think I might well give one of these a try...

 

[Wayland]

I don't think you will be disappointed.

 

[Gailainne]

Excellent write up Gary, looking forward to getting mine.

 

[Wayland]

I've just been back up the hill and taken bearings from the other end of the the wandering church.

Sure enough, there is the half degree inaccuracy. The symbol is definitely in the wrong place on the map.

I don't think I've ever owned a compass more accurate than a 25K map before....

 

[pteron]

It could be one of the deliberate inaccuracies that OS introduce to catch people copying their maps

 

[EdS]

very temped by the damped version - have you got a link?

 

[Doc]

I like this.

I've already got a Silva Type 54 (actually badged Brunton, but it is made in Sweden by Silva) and it will measure bearings to 30 minutes or so. But it won't measure vertical angles, and I can think of times when this would be useful.

I guess if you sight Polaris you can work out your latitude?

 

[Martyn]

I don't think I've ever owned a compass more accurate than a 25K map before....

Have you ever used a Franny Barker? Beautifully damped, no bubbles, reliable, fast and accurate to 1/4 deg unsupported or even less if you support it (down to 4 minutes of arc with the mills version scale, +/- 15 minutes of arc guaranteed by Psyer-SGI). The Sylva type 54 is almost as good, either will deliver accuracy well beyond the point of usefulness.

 

[ged]

I guess if you sight Polaris you can work out your latitude?

Well you'll also need a good horizon, or at least a bucket of water.

 

[Doc]

Not with a bubble sextant. I'm wondering if a pocket transit like Wayland's can be pressed into use for this.


The Francis Barker compasses are very nice, but no good for measuring vertical angles.

 

[Martyn]

The Francis Barker compasses are very nice, but no good for measuring vertical angles.

Very true. How useful is that though? Generally, I dont even bother with declination. If you've got landmarks, you dont really need a compass.

 

[Doc]

Very true. How useful is that though? Generally, I dont even bother with declination. If you've got landmarks, you dont really need a compass.

All very true. Probably not useful for everyday use, but the things I was thinking of were:

Measuring angles of rock strata (dip) - it's original use.
Measuring the heights of trees. Thoreau did this annually to measure growth. I might want to do it when thinking of using a tree as a field-expedient antenna support, though I'm sure a guess would be good enough.
Teaching the kids trigonometry.
Celestial navigation - although it's never going to be as accurate as a sextant. Being a degree out gives you a 60 nautical mile error, so maybe not of practical use, but interesting nevertheless.
Predicting accurate acquisition of signal/loss of signal times for amateur radio satellites in mountain country (the standard software tells you when the bird comes over the horizon- great in the fens, but not here)

Having said all that, I might be just deluding myself in order to justify buying a new toy. And I like scientific instruments.
Did you know it has a vernier scale?

 

[Martyn]

All very true. Probably not useful for everyday use, but the things I was thinking of were:

Measuring angles of rock strata (dip) - it's original use.
Measuring the heights of trees. Thoreau did this annually to measure growth. I might want to do it when thinking of using a tree as a field-expedient antenna support, though I'm sure a guess would be good enough.
Teaching the kids trigonometry.
Celestial navigation - although it's never going to be as accurate as a sextant. Being a degree out gives you a 60 nautical mile error, so maybe not of practical use, but interesting nevertheless.
Predicting accurate acquisition of signal/loss of signal times for amateur radio satellites in mountain country (the standard software tells you when the bird comes over the horizon- great in the fens, but not here)

Having said all that, I might be just deluding myself in order to justify buying a new toy.

Not sure about the above, but this...

...And I like scientific instruments.

...I can relate to. In fact I would possibly consider buying a genuine Brunton Pocket Transit for just that reason alone. It's really the main reason I bought a franny barker as for all practical purposes, the Silva 54 is a more useful compass. I just love the franny barker as a beautiful instrument. I've also got a very nice Russian stereo, oil immersion microscope (used to work in microbiology years ago), though I always wanted a Leica.

Did you know it has a vernier scale?

Get thee behind me Satan.

 

[Martyn]

On the point of sextants, my dad used to be in the royal navy and loves all those toys. So 13 years ago, I bought him an antique sextant for his 60th - £600 worth. I really should learn how to use it, it's a beautiful thing in amazing condition. It probably needs recalibrating now - dunno who does it these days, but they used to get calibrated by the national physics laboratory in teddington and each one carried a proof certificate. Lovely thing, havent a clue how to use it though.

 

[ged]

On the point of sextants ... I really should learn how to use it ,,,

It just measures an angle, although as you've pointed out fairly accurately. A measurement gives you a position line, and like any other position line you need more than one line to get your position.

http://www.amazon.co.uk/Sextant-Handbook-Adjustment-Repair-History/dp/0070052190

The tricky bit isn't using it to make a measurement, but applying all the corrections* and doing the sums to get your position lines**.

* Instrument error, refraction, dip...
**Arcs of circles, which in the absence of errors intersect at your position, but if they really do intersect in practice then it's grounds for suspicion.

I wouldn't waste money on calibrating an antique. You can get perfectly acceptable results when you get to know the instrument and you're never going to do much better than a few miles unless you're on land.

 

[Martyn]

It just measures an angle, although as you've pointed out fairly accurately. A measurement gives you a position line, and like any other position line you need more than one line to get your position.

http://www.amazon.co.uk/Sextant-Handbook-Adjustment-Repair-History/dp/0070052190

The tricky bit isn't using it to make a measurement, but applying all the corrections* and doing the sums to get your position lines**.

* Instrument error, refraction, dip...
**Arcs of circles, which in the absence of errors intersect at your position, but if they really do intersect in practice then it's grounds for suspicion.

I wouldn't waste money on calibrating an antique. You can get perfectly acceptable results when you get to know the instrument and you're never going to do much better than a few miles unless you're on land.

That book looks interesting, I might give it a go just as an acedemic exercise. The sextant I got for my dad looks like this (except it's all brass)...

Dated sometime around 1910 to 1920 I think, it's had some kind of illumination thing retrofitted to it. I'm sure it'd need calibrating before it was any use.

 

[ged]

The sextant I got for my dad ...around 1910 to 1920 I think, it's had some kind of illumination thing retrofitted to it. I'm sure it'd need calibrating before it was any use.

I don't know what the illumination thing might be unless it was to light up the scale so you could read it in the dark. The scales and the screw threads won't change much but if you're adamant about calibration buy the book. It will show you how to do it, you'll learn a lot about the instrument, and will be a lot cheaper than shipping it to NPL. They charged me something like 60 quid to calibrate a 12 inch ruler twenty years ago! You can play around with a sextant to get the hang of it by standing on a hill and measuring horizontal angles. Sort of like using a compass vertically in reverse.