ltcom
Well-known member
Where the 112.5 degrees comes from...
- Thread starter Kukri
- Start date
ltcom
Well-known member
Not how I remember it though.....
thinwater
Well-known member
Makes you wonder why base 10 (metric) is considered so smart compared to a system based on binary (2, 8, 16) or primes (6=2*3, 30=2*3*5).
colind3782
Well-known member
I'll throw Mils into the equation just to confuse everyone!
Mils
Mils are largely used by the military. The original system divides the face of the compass into 6283 divisions (Mils being short for mili-radians, derived from there being 2 Pi Radians in a circle, so 2 x 3.1416 or 6.283 mil-radians). Most Mils compasses however round this up into 6400 divisions for easier calculations. It is how bearings are described for artillery, mortar and tank fire and military handheld compasses use the same system. It can also be useful for determining range and scale – for example two objects that appear to be 100mils apart and are 1000m away from the observer are around 100m apart on the ground.
Mils
Mils are largely used by the military. The original system divides the face of the compass into 6283 divisions (Mils being short for mili-radians, derived from there being 2 Pi Radians in a circle, so 2 x 3.1416 or 6.283 mil-radians). Most Mils compasses however round this up into 6400 divisions for easier calculations. It is how bearings are described for artillery, mortar and tank fire and military handheld compasses use the same system. It can also be useful for determining range and scale – for example two objects that appear to be 100mils apart and are 1000m away from the observer are around 100m apart on the ground.
Kukri
Well-known member
If the one in the middle were drawn from the outside of the crooked thumb you would have 11.25 degrees.
Refueler
Well-known member
Not being rude ... but we all know that ... what the question is : Where does such a number come from. Which answer is of course from Compass Points.
fisherman
Well-known member
Blame the babylonians for the 360 deg circle. Napoleon would have made it 100degs, along with his ten day week, a 'decade'
JohnGC
Active member
Napoleon made it 400. There are 100 gradians in a right angle.
Ohlin Karcher
N/A
Why don't they just use degrees and decimal degrees? I am struggling to see the advantages of mils, and there are rules-of-thumb for degrees as well. Mils must surely be in use because of a historical accident , traditionalism or somesuch..and now it would be hard to change perhaps.
Ohlin Karcher
N/A
So 360 degree circles were in use long before a minute of latitude equalled a nautical mile. So a nautical mile must ultimately be derived from the old Babylonians . Clever chaps!
anoccasionalyachtsman
Well-known member
I read up on this a few years ago as part of exposing a 'Walt'. My recollection is that it's basically because a degree is way too big for shooters and the hexadecimal division not the simplest for everyone. Base 10 makes calculation far easier to teach.
Ohlin Karcher
N/A
Aha thanks for the info.
PuffTheMagicDragon
Active member
One of the first uses of a pair of compasses that one learned when starting geometry at school was how to bisect an angle.
Refueler
Well-known member
Quite simple really ...
If you go into mathematics - the Radian is a serious component of many circular and spherical formulae. Its not based on anything except the circle itself.
As we come forward in 'evolution' - you will find that many computations use Radians rather than degrees.
The post before bringing fwd the MILS explains its use and its greater accuracy for the gunners etc.
fisherman
Well-known member
...ahem....astrology? #21
Skylark
Well-known member
I enjoy these threads as they have me reaching for two of my favourite books, Bowditch and Oxford Companion to Ships and The Sea. Both have interesting etymology of point. Still not really sure who joined the dots to determine that degrees, distance and time are different ways to express the same thing.
I'm intrigued by Mill. It's mentioned in Bowditch but not The Companion. In the example quoted by Colin, 100 Mills is 5.77 degrees so by simple trigonometry the distance apart of his two objects are 100.4m - so the military are correct
I'm intrigued by Mill. It's mentioned in Bowditch but not The Companion. In the example quoted by Colin, 100 Mills is 5.77 degrees so by simple trigonometry the distance apart of his two objects are 100.4m - so the military are correct
JumbleDuck
Well-known member
Revolutionary France tried 400 gradians, or gons, in a circle. They were never much used, although my ancient TI-33 calculator (1978?) does them.
JumbleDuck
Well-known member
Mils are actually milliradians, and the length of a circular arc is radius x angle subtended in radians (hence circumference = 2 pi r). For small angles, the arc (curved) and chord (straight) lengths aren't very different, so two objects 3km away and 100 mil apart have about 300m between them.
JumbleDuck
Well-known member
Should be astrometry.
snowbird30ds
Well-known member
Base 10 is good as it's easy to count on your fingers for us simple folk, in norfolk they use base 12 as better for counting on toes......
And the babylonians had a great way of counting to 60 on two hands involving the 3 joints on each finger on one hand countable with the thumb giving twelve, multiplied by 5 with the digits of the other hand, it's easy and works well.
And the babylonians had a great way of counting to 60 on two hands involving the 3 joints on each finger on one hand countable with the thumb giving twelve, multiplied by 5 with the digits of the other hand, it's easy and works well.