M73 Prismatic Compass

[Mr Adoby]

The main reason to use a compass with mils is that this approximates the 2 pi radians used in geometry. The circumference of a circle, remember?

http://en.wikipedia.org/wiki/Circumference

http://en.wikipedia.org/wiki/RadianAnd the anglular readings in radians can be directly used for different navigational and distance estimations and calculations in your head, without the need to convert from different ways of measuring angles. This could be used to very quickly direct fire, for instance.

http://en.wikipedia.org/wiki/Radian
http://en.wikipedia.org/wiki/Angular_mil

But if all you need is to find your way through the woods, then I find it hard to see how it could matter if you use 360, 400, 3600 or 6400 degrees.

 

[malcolmc]

I’m a bit uneasy about some of the comments on accuracy of compasses in this thread. My perception is that, for a plain scale, accuracy is a function of the size of the scale irrespective of units; a 3” (75 mm) protractor is going to be less accurate than a 6” (150 mm) one. With compasses there are additional factors such as declination and local magnetic variation. Any time I’ve used a pocket compass to take bearings to establish my position there has always been an error of around a couple of degrees, it’s why 3 bearings taken from a fixed point never cross at a point. It’s not a problem so long as the error is recognised and taken into account, such as aiming off the feature you’re travelling to. Military types need mils scales for their own purposes (mind you, the though of using a pocket compass for gun laying really does scare me!) but civilians use civilian maps and they are marked in degrees - it makes very good sense for a civi to use a compass calibrated in degrees. To do otherwise increases your workload, probably fine in good conditions when you’re not tired, but not ideal at the end of the day when it's starting to rain.

Just my thoughts on the matter.

 

[DKW]

I’m a bit uneasy about some of the comments on accuracy of compasses in this thread. My perception is that, for a plain scale, accuracy is a function of the size of the scale irrespective of units; a 3” (75 mm) protractor is going to be less accurate than a 6” (150 mm) one.

Exactly.

Military types need mils scales for their own purposes (mind you, the though of using a pocket compass for gun laying really does scare me!)

They don't. Gun laying is done by the scale onboard the gun. Huge diameter scale, compared to a handheld compass. Normally the outcome is doublechecked with all other guns in the group/battery, aswell as checked with an observer or a firemissionsvehicle. ALl of wich are equipped with very accurate compasses specifically designed for the job, aswell as armytype gps systems.(accurate!!)

The handheld compass is merely for the footsoldier to lay out a firingorder. To do so the battery needs an approximate direction of observation, in order to shoot the battery in on the target. (they basically need to know what is forward, and what is left and right, as seen from your place.)
No need for 1 mil accuracy for that

Just my thoughts on the matter.

Good thoughts. I agree

 

[malcolmc]

...
They don't. Gun laying is done by ...

Very pleased to learn that .

 

[DKW]

Very pleased to learn that .

Im pleased to set your mind at ease about it

If they did do it though, even i would curl up in my foxhole

 

[BOD]

...but civilians use civilian maps and they are marked in degrees - it makes very good sense for a civi to use a compass calibrated in degrees. To do otherwise increases your workload, probably fine in good conditions when you’re not tired, but not ideal at the end of the day when it's starting to rain.

Just my thoughts on the matter.

Many years ago in the SW of West Australia we were sent on an exercise. We camped the were told our objective. Maps provided were in degrees and we made our route cards accordingly.

Just before setting out the next morning, the instructors came and gave us mils compasses.

No idea why it was done other than to mess us up and increase the stress. Since we were already sleep deprived and poor with mental arithmetic, people were lost all over the place.

And then we were ambushed