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Gravity will pull your laser into level with the curve of the earth Oz, that's why standards and tolerances allow you a few mm here and there ;)
PS. Something that I've always been astounded with is the lurnar method for measruing longitude - and the ability of early sailors in using it without a watch :confused:
Very close Woodborer,
You forgot to take into account the magnetic variation applicable to the particular map being used.
The bearings taken with the compass are magnetic bearings but before you plot them on your map you must convert them to grid bearings (either before or after you add or subtract 180 degrees).
This is because magnetic north, true north and grid north are all different and the variation must be considered.
Magnetic variation will be shown on the map and will be correct for a certain year, usually the date of survey. The variation will change, usually annually or bi annually and must be multiplied by the difference in years between when the map was correct and the year you are geographically embarressed.
To convert from a magnetic bearing(one taken with a compass) to a grid bearing(one plotted on a map) you add the variation. To convert from a grid bearing to a magnetic bearing you subtract the variation.
These conversions are for a map with an easterly variation(which will also be shown on the map) and you simply do the opposite for a map with a westerly variation.
Eastie I think you didn't understand Dr Ozwinner's statement.
He uses a laser to put people on the level whilst performing his brain surgery. The dimensions would be neurons not mm.
- Wood Borer
Jack,
You are quite correct if your compass reads magnetic but most good compasses read true. You can change the variation on them so they read true.
I have a handheld Suunto compass that I have calibrated for true in these parts (approx 11 degrees East). Mine is also designed for the Southern Hemisphere for the Australian region this keeps the needle almost horizontal instead of dipping.
On the yacht we had a fluxgate compass which I adjusted for both variation and deviation which made the calculations a bit simpler especially in rough seas when you are half asleep.
It sounds like you already knew how to do determine your position using a compass when you asked the question.
- Wood Borer
Sorry Eastie, I can't make out whether you are meant to be joking here or not. :confused:Quote:
Originally Posted by Eastie
Psst Bob.Quote:
Originally Posted by Bob Willson
Easties gone to the great cat killing field in the sky, remember? :(
Al
The beam of a laser does not follow the curvature of the earth and given ideal conditions will remain straight whilst the earth gradually falls away below it.
Unfortunatly for lasers they are badly effected by refraction in the air.
When two layers of air of different temperature meet the interface between the air masses acts as a lens and bends the laser beam.
This can be seen on a hot day as a shimmering in the air.
As any big bore shooter would know, the effect can be quite large over a longer range with errors between apparent and the real location of the target being measured in +-metres over 1000m range.
Wood borer,
I wish I had an adjustable compass instead of the old prismatic from WWII, that would make life much easier!
I did know the answer to the question. It would be silly of me to post a question on a QUIZ thread if I didn't know the answer myself.
Jack.
Just a little bit of trivia, slightly off topic (but prompted by the laser levels and earth's curvature).
The two towers of the Golden Gate Bridge (largest suspension bridge in the world) are perfectly plumb but are not parallel. Because they are so far apart and so tall the curvature of the earth means that they lean away from each other whilst being perfectly plumb. (Hint to Al, use this as an excuse next time something's out of whack :p :D )
Mick the trivia master :rolleyes:
So Mick the leaning tower of Pisa is vertical but just not at the place where it is located.
Your theory (which I understand and agree with) suggests that buildings should be wider at the top than at the base if the walls are vertical. The top floor would therefore have a larger area than the ground floor.
Is this why people pay more for penthouses than basements? :D
Perhaps Al takes this into account when quoting on jobs.
- Wood Borer