Military aircraft compasses

[boguing]

I have a bit of a puzzle on my hands, and wonder if any of you can help.

Somebody tells me that some military aircraft had their compasses graduated in Mils rather than degrees.

I'd never heard of Mils, but for those that haven't either they should be a thousandth of a Radian, but since that would give an awkward 6,283 in a full circle, it's been rounded to 6,400. As far as I can tell, the main reasons that they're used are for greater accuracy when shooting at longer distances and for the quite useful fact that anything 1,000 units away from you measures one Mil on the scale when it is one unit long - so one foot at one thousand feet range (slightly inexact because of the rounding). One degree is about 17.8 Mils, so you can see how handy that accuracy is if you're trying to hit something small a mile away.

My question then is whether any of you have ever seen or heard of an aircraft compass graduated this way? Would Army aircraft or maybe the RN have used them and so possibly the FAA? If it helps, the era that he was referring to is really mid 60s to late 80s.

[B2N2]

Nothing I've ever heard of.
I'm thinking maybe a gunsight mounted near the compass or on the compass.

[Two's in]

Army prismatic compasses (ground use) were available in mils, degrees, or some had both on a split scale. Artillery and surveyor types used the additional accuracy of mils, average squaddies who struggled to tell the difference between the sun and the moon were generally fine with degrees.

[Roadster280]

I can't speak for aircraft compasses, but I only ever saw issued prismatic compasses in mils (R SIGNALS). Bit of a waste when the calibration marks on the antennas were in degrees!

[SpazSinbad]

The A-4 Gunsight was as good as a compass and it had MILS for accuracy - dial on left. LIBRAscope reticule below (bat****crazy)

Librascope Reflector Gunsight used in early Douglas Skyhawks.
“...In the early fifties, the Librascope Co. designed a Reflector Gunsight that was used in the early versions of the Douglas A4D Skyhawk. This Sight had been in production since about 1953 and the quantities manufactured probably numbered into the thousands. Up until 1969 only a few subtle changes had been made such as, moving the turn and bank indicator up to the bottom of the reflector plate for improved visibility and changing the reticle pattern (probably partial instead of complete circles, and vertical and horizontal radii). In 1969 major changes were made in the mils depression knob, reflector plate support strut, locking lever, etc. by the Naval Avionics Facility, Indianapolis, Indiana. They produced a number of kits for modifying the old sights to the new configuation. In 1970, these changes were incorporated into new sight production....” http://www.aircraft-gunsights.com/reflector-sights/

OLD Style Gunsight SITE: http://www.aircraft-gunsights.com/reflector-sights/

http://i98.photobucket.com/albums/l261/SpazSinbad/NewNewAllBum/A-4gunsightNATOPSforum.gif~original (http://s98.photobucket.com/user/SpazSinbad/media/NewNewAllBum/A-4gunsightNATOPSforum.gif.html)
http://i98.photobucket.com/albums/l261/SpazSinbad/NewNewAllBum/A-4gunSightMILS.gif~original (http://s98.photobucket.com/user/SpazSinbad/media/NewNewAllBum/A-4gunSightMILS.gif.html)
http://i98.photobucket.com/albums/l261/SpazSinbad/NewNewAllBum/a-4librascopeReticuleEDforum.jpg~original (http://s98.photobucket.com/user/SpazSinbad/media/NewNewAllBum/a-4librascopeReticuleEDforum.jpg.html)

[Sloppy Link]

Mils are extensively used by ground troops as has been said, for accuracy but also a useful tool for range estimation. Your forefinger held up at arms reach is about 30 mils, therefore, if the target is at 2,000m and the fall of shot is two fingers away, the correction is "right 120". Further, the graduations in binoculars are 10, 5 and 2 mils, therefore, if you sight a BMP-1 (2m to the top of the hull) and it fills the 2 mil graticule, you know it to be 1,000m away.
Or zap it with a laser range finder.....and his laser warning receiver will tell him you are looking at him and attract unwelcome attraction.
Interestingly, the Soviet Bloc use mils also but rounded down to 6,000 mils in a circle.

[topgas]

average squaddies who struggled to tell the difference between the sun and the moon were generally fine with degrees.

Tha Army uses mils calibrated Silva compasses for teaching navigation

https://www.army.mod.uk/documents/general/Navigation_jun11.pdf

although the compass does have an inner scale in degrees
https://www.goarmy.co.uk/silva-compass-made-for-the-british-army-prod

[Timelord]

Every aircraft compass that I have ever seen has been calibrated in degrees. Gunsights, on the other hand, have their depression measured in mils.

[boguing]

Thanks for the replies so far, and in particular to SpazSinbad for the lengths he's gone to.

I should have made it clear that my interest is in compasses used for steering. And, more specifically, the fact that I may have cornered a 'Walt'.

He claims to have flown Sea Vixens and also mentions Meteors. I had my doubts, so mentioned that I had an E2.B (a standby compass that he would probably have sat behind). He blustered a bit over what an E2.B might have been and so I told him it was a compass. His immediate response was to ask whether it was graduated in Mils or degrees, and went on to explain that you had to know which it was when being given a course to fly. At which point the rat became a bit smellier.

[Herod]

I reckon you've got your Walt. The E2b is/was in degrees. Ordinary pilots know nothing else. In fact IIRC, the E2b is only graduated in ten-degree increments. Now, work out the most embarrassing way to out him. Could be fun.

[SpazSinbad]

First page of this pdf has this photo of the 'roger - standby' Sea Vixen compass:

http://www.seavixen.org/images/documents/Pt6._2._Cockpit_photographs._893_Sqn_Museum_Piece._Best_Avai lable_Feb_2011.pdf (1Mb)

http://i98.photobucket.com/albums/l261/SpazSinbad/NewNewAllBum/SeavixenStandbyWetCompassTOPwetFORUM.jpg~original (http://s98.photobucket.com/user/SpazSinbad/media/NewNewAllBum/SeavixenStandbyWetCompassTOPwetFORUM.jpg.html)

[ORAC]

Might want to ask him what the main compass was...... Mk. 5FT...

Sea Vixen FAW Mk 2. Pilots Notes. (http://www.seavixen.org/seavixen-technical-documents/faw-mk2-pilot-notes)

http://www.seavixen.org/images/documents/5.Flt_Instruments_and_Compassesscan0001.pdf

[Basil]

Never known a steering compass, aircraft or marine, to be graduated in mils. The only occasion I've seen them was, when in REME attached to an artillery regiment, the gunners used them for gunlaying.

[Fareastdriver]

It used to be a regular on 1st April----the decimal compass. Here it would be explained that the military were going over to decimal compasses so East would change from 090 to 025 and so on. Some excellent facsimiles of decimal compasses would be produced, some quite convincing.

Ask any navigator; they would have done a course on them.

[boguing]

The reason that I have an E2B is that my Pa designed an aircraft compass and consequently had a bit of a collection of others, that I now have. With that background I've flown a little, sailed a lot, and could see that introducing a second number system would be a) a bountiful source of interesting moments, and b) thought to be an excellent idea by someone in a Ministry office somewhere.

I wonder if a bunch of Sea Vixen pilots fancy a day out in Surrey?

[pasta]

Other than surveying and gun sighting, it's hard to imagine anything that could be done to an accuracy of a degree or better; certainly not steering a moving object of any kind.

Off topic: In my sailing days, we used to use gimballed compasses that were weighted to compensate for the dip of the magnetic field. This meant that you had to swap them over when you went to the Southern Hemisphere...

[boguing]

They still are weighted pasta, and I don't know if you noticed but it leads to a problem which is known about in flying and more or less ignored in sailing. That added weight gets left behind if you move sideways. In boats it makes steering South harder, but in a side-slipping aircraft it's possible to fly in a complete circle with the compass apparently motionless.

My Pa's idea was to remove the weight but to stop the needle from dipping.

[ORAC]

Other than surveying and gun sighting, it's hard to imagine anything that could be done to an accuracy of a degree or better; certainly not steering a moving object of any kind. That's the old joke, isn't it?

Nav: "Starboard 1 degree".

Pilot:"I can't adjust by just one degree".

Nav: "Roger, starboard 5 degrees".

Pilot: "Steady".

Nav: "Roger, port 4 degrees"......

[KenV]

Other than surveying and gun sighting, it's hard to imagine anything that could be done to an accuracy of a degree or better;I'm pretty sure that should read "precision" rather than "accuracy". The difference is subtle, but oh so important.

[Tankertrashnav]

Other than surveying and gun sighting, it's hard to imagine anything that could be done to an accuracy of a degree or better; certainly not steering a moving object of any kind.

Which was something I used to ponder on when doing a compass swing on a raw Norfolk February morning out on the airfield. I cant remember the accuracy of the headings I passed to the nav inside the aircraft after reading them off the Watts Datum Compass, but I am sure it read to less than 0.1 of a degree. Could never see the point of that, nor the laborious Fourier's Analysis which followed the swing. But then I was only a hack squadron nav - maybe somebody more versed in the mystical art of navigation might enlighten me!

[Blacksheep]

The datum compass did indeed read in tenths - but it had uses beyond RAF Compass swings, in surveying.

The datum compass also required scheduled calibration and at Changi we used to swing the Watts Datum on an open area that doubled as part of the golf course. One day the inevitable happened and it was hit by a golf ball. I won the draw out of the hat for the trip to the Admiralty Compass Laboratory in UK to have it repaired - which gave me two weeks "leave" while it was returned to serviceability - one week at home and a second week in the "Route Hotel" at Lyneham, waiting for a flight. I promoted myself to commissioned rank during my stay, as the food was so much better in the officers' dining room and they had free newspapers in the lounge: nobody from the staff seemed to notice, and if they did they never said anything.

[pasta]

They still are weighted pasta, and I don't know if you noticed but it leads to a problem which is known about in flying and more or less ignored in sailing. That added weight gets left behind if you move sideways. In boats it makes steering South harder, but in a side-slipping aircraft it's possible to fly in a complete circle with the compass apparently motionless.

My Pa's idea was to remove the weight but to stop the needle from dipping.

I never really thought that through, but it's blindingly obvious now you point it out.

How does your Pa's compass stop the needle dipping without inhibiting its rotation?

KenV - you're right of course - precision is the correct word, and I'm kicking myself for getting pulled up on that one. Particularly with regard to compasses with their many sources of inaccuracy...

[Sevarg]

I seem to remember being told that German compasses captured after the 39/45 unpleasantness had 400 degrees. Anyone know for sure?

[50+Ray]

I brought back a prayer mat from Saudi which had a built in compass to ensure kneeling towards Mecca. It has 400 degrees:-(

[Sevarg]

One of Goring's flying carpets?��

[boguing]

I never really thought that through, but it's blindingly obvious now you point it out.

How does your Pa's compass stop the needle dipping without inhibiting its rotation?

This is the early '50s prototype. The magnet is under the pointer and atop a long thin and very light shaft which runs through a jewel bearing in a plate near the top and on down to another at the bottom. To put it simply, the needle just can't dip and any sideways load on the bearings is too small to matter.

https://lh3.googleusercontent.com/qJyb2Rhaj_mzLdgLNc6blXJ2W9vH4LOJOOAKHhLf_pwLpTPg0P2zqeUW858m m_U21BU0WoEShT_EFDE0lPd4PufZERBZYQVO24M0QQ8G0aRIFjfnS3rU1yU0 3lbF1jhUq-rv88sxHTUVDs58mIckgRXYQyY4L3TMOJMXllkRi26jcopzVyCl_Xe14pFlqv 7W746F4wdw-_YWPsamd06VXUu3dTtU0NzcJ7--LAfD-yWXr_qe1ee8fJ4e1gcYvdLDSnonyA7ZRoYoxsLHVQ1fZiBzDu00hnmgZam9o wojUORTJyzHdPoDP-eULTF5xU48AKk5EkNmwApEO_45uzhuLzxq3nDTo8H86cbWs45WFvs8kq-KNj-kF2-WyB18_VwJHLrEcl9AoUApOf0-DkdH6mrgwSKDue8_L94YxNFyhu5AXmMcf-w6tjm5otQpRyLbD0Ahk4u_vUDTt24PKVTKHa1PetX8oir6Uw3dgXtz65tsyF IU1br2X2eLRqbuKmsjpyPd5E1Z97sOplB0SRANvx5aXUdGHXS2a0Ki932_mf ipuPT2yv8xbwwB4tKqoj77gNIWc2I1SP1M3xCTVRo-jOdc0DVztkWcvZn0x6XKKV7ldEUvsCSc=w661-h496-no

It was designed for use in gliders - early units were loosely mounted so that they could be tilted to match the bank angle in thermals. Later units got an external gimbal. The advantage over a floating ball type was the very low inertia, and they were pretty popular until the fluxgate arrived.

[Sevarg]

Er, south's ok but east west seem to have transposed or have I have a glass or two?

[boguing]

Er, south's ok but east west seem to have transposed or have I have a glass or two?

Have another glass and then imagine flying with it...

[KenV]

Since the numbers are all "backwards" and E and W are opposite to where they "should" be, does that mean the needle is stationary and the dial rotates about the needle?

https://lh3.googleusercontent.com/qJyb2Rhaj_mzLdgLNc6blXJ2W9vH4LOJOOAKHhLf_pwLpTPg0P2zqeUW858m m_U21BU0WoEShT_EFDE0lPd4PufZERBZYQVO24M0QQ8G0aRIFjfnS3rU1yU0 3lbF1jhUq-rv88sxHTUVDs58mIckgRXYQyY4L3TMOJMXllkRi26jcopzVyCl_Xe14pFlqv 7W746F4wdw-_YWPsamd06VXUu3dTtU0NzcJ7--LAfD-yWXr_qe1ee8fJ4e1gcYvdLDSnonyA7ZRoYoxsLHVQ1fZiBzDu00hnmgZam9o wojUORTJyzHdPoDP-eULTF5xU48AKk5EkNmwApEO_45uzhuLzxq3nDTo8H86cbWs45WFvs8kq-KNj-kF2-WyB18_VwJHLrEcl9AoUApOf0-DkdH6mrgwSKDue8_L94YxNFyhu5AXmMcf-w6tjm5otQpRyLbD0Ahk4u_vUDTt24PKVTKHa1PetX8oir6Uw3dgXtz65tsyF IU1br2X2eLRqbuKmsjpyPd5E1Z97sOplB0SRANvx5aXUdGHXS2a0Ki932_mf ipuPT2yv8xbwwB4tKqoj77gNIWc2I1SP1M3xCTVRo-jOdc0DVztkWcvZn0x6XKKV7ldEUvsCSc=w661-h496-no

[boguing]

KenV, you're going to kick yourself!

Nope, numbers are fixed to the body. Body fixed to glider panel and the needle stays pointing North.

Imagine flying North and turning right ninety degrees.

[boguing]

Here's the E2.B which was the original subject of the thread. Numbers seem to go the wrong way on it too, but it works!

https://lh3.googleusercontent.com/QTxbrCQOrrB8cpPo7X-9cAdfF-e9xH3q1KwcVAMNWeimGPN4a1eu_A4nRKBAtpjWA023RcxuUqOxilyepKN1ne lg_JKuF-TSwPGczeg78qIjp3Cwdje2190UdlFlHL-yCEadvhpKi9p-VIRyT226p-yChkz2CvxqIlQPzmY2iaH5r5o-5ZOMdMqz6ORcoB9Rvop_OnOlsYPTvHVSYrIKXIlkHpC0w4OWSxBAehl_oagu g6WRWdT9QwzgHRQbU0oaF97XK3d7Dex7c4hgOdEk7352IhRYBpRKcoxuT1fN gw4bbsNxQm36hDOc0ZxaSbn6usJ3H-DgXD1rnjuoFVe7ANxWsKZoQDjlh1S91KbhgZgvYCTyJ20My5elh_3-o2HQk3AX066xyXRuumDByHzubI6ycvl7YL-bZGVgQiA_ycGX8sX1ea9uuBfI2dAwpbCG-2K1mLPQwCt2bwijQOqHwOPik1kSYREhIWnYdabbLkCX5x3sj6Fnhtsg2mH7D x65-c0QNu4nSUnJIOTgIdp8QI7fIGiJFQPoWzUBrTcznuyEKFiJJQoJIUDFVwX5j hpyo2SKTd9r-DP2SW7H6p_at3ennHU4V64ap9JsMwXO8EVfyHFsVz9w=w661-h496-no

[Sevarg]

Yep, another glass worked.

[Fareastdriver]

The original gyroscopic Direction Indicator had a couple of numbers visible through a window on a horizontal disc which you flew around. You had to cage it after landing, during aerobatics and then reset it to a massive compass between your legs.

All this with no autopilot!

[Herod]

Fareastdriver. Chipmunk?

[boguing]

Camera's busy this evening chaps.

From a Chippie.

https://lh3.googleusercontent.com/ViiOSW30tPR64oyRH9jHO8sNWNk0S6CeST5ExDzd1GGqhVa4VJEjsisQcpzW 1eS7NrbxhFctoMAglOO151GGGgw-3Ug4IJW7-8eavgeV6xwuBDhNH-_oeGfQoruiSJjxgyUGRi8ilfY-8jZeQkUjbaqXiHrr_qyOFFx17qoVCAw417JTHPIfv9yLpfsTdA5iMh-ytvceOyfJTvsPa8qSikEYV2yCxyt1yHaRtkqCVSwUwKEAimsrrgkA0X4YVDz tyaXTrS6GegOWApYrMXkO2yjRSRqOMq5Ml3I33_5oPoKg8X55dgOTlgfKTfH Feg9hICPSXoBlWvvfLFePqR1F6YaxN_Xx5MK9mG2CFIwpMgx41SNwIjNuVKL SrTe8O3NLDsDLnpwzejtnrDycArQknGruu_X4KWkoFzF12GjchG7TVAaLbTt 1IouUpExpCyq_wIHGc5ZDJhppB27smIIReeKsUQ9cllgLpEn7VeovuX5fR-TNeWOO7H0UAunspa08cVskPo_2aPA8g07kP977UvDkLTVP9fXUtFCLqrs9yb-qd3HUbRltloghRpvxfnGwquMjjsJx4CnzHyoZmRAFbo6DpUuTiOhqqCLbDPt wrIcgN_8IKTft=w661-h496-no

[Two's in]

Seeing that Chippie directional Gyro reminds me of when I was intellectually challenged in first trying to fly and think simultaneously. I used to have imagine a string tied from the top of the stick to the heading I wanted to turn on to so you would "pull" the compass heading over to the lubber line. In this case, to turn from a Northerly heading to 330 you would "pull" the string to the left until the number came around!

[SpazSinbad]

IIRC the story about an A4G pilot hitting the gunsight during an arrest onboard MELBOURNE has been told elsewhere. Sadly 'Neptunus Lex' the USN NavAv story teller is no longer with us whilst some of his old stories have been archived here: https://thelexicans.wordpress.com/2016/01/30/the-best-of-neptunus-lex/ I could not find the '8-day clock [& wet compass]' story so here is the last bit about it - Skyhawkwise after a 'utility hydraulics failure'.
Face to Face with the 8-Day Clock [& Wet Compass] 23 Apr 2011 Neptunus Lex

“...I chose an off-duty runway for my straight in approach, and lowered the arresting hook to engage the approach end arresting gear. The wheel brakes would still have worked just fine, but without wing spoilers the Scooter could be a little tricky to handle on deck at high speed.

I had by that time a few hundred arrested landings, most of them in the FA-18. In the Hornet you were supposed to lock the restraint harness that kept you strapped securely in the ejection seat before landing - it was part of the landing checklist - but it was not big deal if you didn't: There was an inertial reel incorporated within the seats of all carrier aircraft that would sense sudden decelerations and apply the brakes. The Scooter had one too.

Only that inertial reel, like my poor, wounded utility hydraulic line, was also 35 years old. I landed safely at about 125kts, took the gear at maybe 115 or so and was thrown violently forward in the cockpit, getting a face-full of the 8-day clock [& wet compass] mounted on the canopy as the airplane came to a sudden stop, the arresting wire snaking and hissing behind it. It was a sunny day, fortunately, because my helmet visor was down and took the brunt of the collision, cracking in two places, or otherwise I would present an entirely different face to the world to this day. I was momentarily stunned and a little bruised, but none the worse for wear as the aircraft ticked down in the cable and the fire trucks raced up alongside me.

And I wasn't feeling quite so smug about checklists.”

http://www.neptunuslex.com/2011/04/23/face-to-face-with-the-8-day-clock/
OR: https://thelexicans.wordpress.com/2016/01/30/the-best-of-neptunus-lex/
http://i98.photobucket.com/albums/l261/SpazSinbad/NewNewAllBum/A-4EFGKclockCompass.gif~original (http://s98.photobucket.com/user/SpazSinbad/media/NewNewAllBum/A-4EFGKclockCompass.gif.html)
http://i98.photobucket.com/albums/l261/SpazSinbad/NewNewAllBum/A-4clockCompassFRONTtifFORUM.jpg~original (http://s98.photobucket.com/user/SpazSinbad/media/NewNewAllBum/A-4clockCompassFRONTtifFORUM.jpg.html)

[John Eacott]

Thanks for the replies so far, and in particular to SpazSinbad for the lengths he's gone to.

I should have made it clear that my interest is in compasses used for steering. And, more specifically, the fact that I may have cornered a 'Walt'.

He claims to have flown Sea Vixens and also mentions Meteors. I had my doubts, so mentioned that I had an E2.B (a standby compass that he would probably have sat behind). He blustered a bit over what an E2.B might have been and so I told him it was a compass. His immediate response was to ask whether it was graduated in Mils or degrees, and went on to explain that you had to know which it was when being given a course to fly. At which point the rat became a bit smellier.

Have you bailed him up yet? If you feel like throwing another spanner in his works, ask him what is the difference between and E2B and an E2C ;)

The aircraft compass system used in the Wessex HAS3 and the Sea King HAS1 was derived from the TSR2 and was a wonderful piece of kit in the Wessex, with a large cockpit display and easily flown to 1 degree increments. For some bizarre reason the same compass system in the Sea King saw the display replaced with a tiny instrument calibrated in 5 degree segments: made GCA and other IF work quite a challenge!

But always in degrees, as already opined by others.

[Dan Winterland]

Other than surveying and gun sighting, it's hard to imagine anything that could be done to an accuracy of a degree or better; certainly not steering a moving object of any kind.
Which was something I used to ponder on when doing a compass swing on a raw Norfolk February morning out on the airfield. I cant remember the accuracy of the headings I passed to the nav inside the aircraft after reading them off the Watts Datum Compass, but I am sure it read to less than 0.1 of a degree. Could never see the point of that, nor the laborious Fourier's Analysis which followed the swing. But then I was only a hack squadron nav - maybe somebody more versed in the mystical art of navigation might enlighten me!

On arrival at an FTS, I was informed I was going to be the new 'Navigation Officer' - the reason being that the job was vacant and it was known that my dad was a navigator. This role involved being the consultant on all things, navigational (ha ha - I failed my first attempt at the FNT!), teaching the students their navigation ground-school - and horror of all horrors - doing compass swings!

On a cold winter's morning standing in the slipstream of an aircraft at full power, I think it unlikely if any heading we recorded was within 5 degrees. And as for a Fourier analysis, I scraped a C at O level maths, so that's all I'm going to say about that matter.

As approximately half of all RAF pilots passed through my hands between 1990 and 1993, I'm probably more responsible for the decline in RAF pilot navigation standards than anyone else!

[Dan Winterland]

It looks from the Sea Vixen photos that it had AHARS (or the AI and Compass fed from the MRG in non commercial speak). You could ask your Walt about that - he would know if he flew the thing.

I have never heard of an aircraft having a compass calibrated in mils. I used them in the Army, IIRC a mil was tens yards displacement at 1000 yards. Useful info if you are trying to drop a mortar bomb on someone's head.

[ORAC]

Dan, see my link on page 1.

http://www.seavixen.org/images/documents/5.Flt_Instruments_and_Compassesscan0001.pdf

[ORAC]

Aeronautical Compasses - Compass Museum (http://compassmuseum.com/aero/aero.htm)

[boguing]

Aeronautical Compasses - Compass Museum (http://compassmuseum.com/aero/aero.htm)

ORAC, I'm a bit stunned. Pa's compass is on that page, and it describes him as a WWII 'Ace'. So I've just checked on Wikipedia and he's on the list there. The thing is that he didn't tell me anything about it. He led me to be believe that he was an occasional flight engineer and I was under the impression that he didn't learn to fly until he took up gliding post-war.

I'm not sure it's right, so I suppose that I need to get in touch with RAF records - something I've meant to do but not got round to.

Don't know what to say really.

[Dan Winterland]

ORAC - that seems to be the system.

[Pozidrive]

I seem to remember being told that German compasses captured after the 39/45 unpleasantness had 400 degrees. Anyone know for sure?



That's certainly a common system for surveying in Europe, called Grads or Gons, most pocket calculators can be switched to that option. 400 to a circle, 100 to a right angle, then decimals rather than minutes and seconds.


Dangerously close to the familiar 360, so its worth checking if your last numbered figure is 350 or 390!

[Pozidrive]

...IIRC a mil was tens yards displacement at 1000 yards. Useful info if you are trying to drop a mortar bomb on someone's head.


Its 1 in 1000, all explained in Post #1. Did you always miss?

[ACW418]

John Eacott,

You have a PM.

ACW

[Mechta]

If you watch the weather forecasts after the BBC News in the UK, you will be familiar with Sarah Keith-Lucas. Her great grandfather Keith Lucas, who worked at the Royal Aircraft Factory, invented the aeronautical compass, and following his death in a flying accident in 1913, a road in Farnborough was named in his honour.