Sounds like you are having fun! With a map/chart and a hand held compass (not a cheapo in some survival knife kit) I can navigate around on land OK. Since I do not know how to use a sextant I would be lost at sea. Even without a compass I can find N-S-E-W on a cloudless night or during the day.

I have had those cheap dash mounted magnetic compasses in several vehicles and if they are adjusted properly they do well enuf to keep me on the right track with a map. Finding a useful place to mount one in some vehicles is difficult or impossible. Some of them have poor mounting means. Illuminating one decently at night is also a problem.

Years ago Radio Shack had a decent flux gate compass.

I still have not found one that will work in the Buick. I would not buy one off ePay due to return/restocking costs.

BTW, you can thank my uncle for the GPS system.

I am still not ready to drop $100-150 on a compass tho.

 

Maybe, if your dead set on a dash mounted compass - get a marine type one mounted on a trimabal, so it can orientate up or down or side to side with the movement of the vehicle (just as it would at sea on a boat)! They are back lit for night nav (usually with a red rubber 'condom' thingy for the globe to preserve night vision at sea) and they often have a sliding cover to protect them from the sun heat when not in use!!

They also have adjustements to allow you to do a basic setup and correct for magnetic deviation within the vehicle to tolerable limits!

After that you could always do a east west/ west east run and north south / south north run, and create your own "deviation" chart for your car / compass once it's adjusted!

OK - next to mess our calculations around is variation.

Maps & charts are orientated to the Earths longitudinal lines and point to true north! A magnetic compass points to magnetic north!

Magnetic north "moves" and we have to correct our magnetic compass reading to allow for two interacting influences:-

1. The "deviation effect" the compass has built in due to the already mentioned magnetic fields within a basically ferrous faraday cage that a car shell represents , as well as it's inherrant electromagnetic influences of it's electronics circuits (Both switched on and off!!).

2. The KNOWN magnetic variation at that point on the Earths surface shown on charts (and maps) on either the nearest printed compass rose (chart) or within the north marker on the map showing the degrees & minutes difrference between magnetic & true north! This allows for magnetic anomalies within the earths crust that effect the compass needle differently in different places! It also varies slightly each year detailed within the compass rose printed on the chart or on the datum and other info of the map which you have to allow for!

So - these two different influences must be applied to any magnetic compass reading taken, to make any observation correlate with the true north orientation of the map chart if that makes sense before information can be used between the map or the chart and vice versa!

So how do you apply those corrections?

East Is Least & West is Best!

If Deviation is East - you subtract it from the magnetic bearing taken before applying it to a plot on the map and if Deviation is West you ADD it to your Magnetic bearing before aplying the plot to your map or chart!

Now - for your Variation the map / chart will show you whether it's east (-ve) or west (+ve) and likewsie you also allow for these corrections to the previous deviation corrected magnetic bearing taken before applying the data to a map or chart plot!

In real world situations it's "unusual" for the combined Deviation & Variation together to add up to more than a 10 degree alteration betwixt magnetic and true - but it does happen depending on the individual compass and the magnetic anomalie (variation) of the area.

Example a -ve 3 degree variation - added to a positve +3 degree deviation would cancell each other out - meaning the el cheapo dash compass is spot on for a "true north" Map reading at that spot in that direction!

But spin 180 degrees and do the same thing and you might find the opposite!

Say a minus (-ve) 10 degree Variation applied And Your cheapo compass is really screwed up and needs a (-ve) Deviation of another 10 degrees when pointing the other way!
Combined - these add up to 20 degrees applied to the magnetic bearing taken to get a true "north" reading for the map!

So to 'correctly orientate' the map while your driving to reflect the compass reading you'd have to skew it 20 degrees to agree with the compass heading one way and it's spot on the other way!! Same road different directions & 2o degrees difference from what the compass map says!

Scarey huh?

We all know theres 90 degrees in a change in direction to the 4 quarters of the compass (NSEW) - and suddenly our compass is 20/90 out...or almost 10% wrong in it's direction compared to our map - thats pretty confusing - especially when you consider these two factors (Deviation / variation) constantly act upon each other thru every change in direction associated with the track / road we are on and it's every twist and turn!

This makes it easy to get lost - the map and the compass to the untrained eye don't appear to agree, which one do you trust? and you end up guessing and take a wrong road and get lost stuck - happens all the time!

Heres something tho - with the little Etrek garmin tho - it can be set to point to true north like your map and will account for variation & deviation real time in it's calculations with its electronic fluxgate compass!

For $40 or $100 - which one do you NOW want to be finding your way bye????

The GPS is a "No Brainer" because apart from being "easier" as a compass to steer bye since it does all the variation / deviation true reading conversions for you, instantaneously, it can ALSO tell you within a few feet EXACTLY where you are at any goven point in time AND how far exactly (and in what direction) to any other known point (and what speed your travelling at and how far left to go and how long it will take at current speed!!

When you think what a $100 GPS can do compared to a $40 dash compass - there is no comparison!

A compass is usefull in the right (expert) hands, if everything else fails - whereas a GPS can make a navigator out of a hillbilly pleb in about half an hours tuition!!

It's really a no brainer - with our fuel price we are talking what - two tanks a gas???

That said GPS for all it's superiorityis ALWAYS a BACKUP navigation device - it ONLY confirms what an experienced navigator has already ascertained from his chart and compass calculations!

Anyone learning anything yet? The real world corrections are often in a few degrees and minutes either way!

The old sailors "aid memoir" TVMDC (True Virgins Make Dull Companions) is what helps us "remember" how to do the mathematics to change from true to magnetic and magnetic to true readings between our compass and our maps / charts!

True reading (From Chart / Map)
Variation Applied (-ve or +ve from the printed compass rose / north marker)
=Magnetic
Deviation (_ve or +ve applied to correct for the compass error)
=Course (to steer/drive)

Just rember this is base 60 maths tho (Degrees, Minutes & Seconds) addition and subtraction!

Remember "east is least & west is best", & "True Virgins Make Dull Companions and basically - you should be able to nut out the rest!

Now how the heck you do that while driving the truck at the same time?
Why do you think Rally drivers have "navigators" huh? Asin sailing & Rallys - it's the navigator wins the race just as much as the nut behind the wheel!

Cheers!

 

capiat qui capere possit