Compass, Maps and GPS
Compasses, Maps and GPS.
NB. This is not a “How to” Guide, but something to hopefully point you in the right direction…
(Pun intended 😉 )
This blog focuses on Compasses.
A very simple and reliable instrument, now consisting of a baseplate and housing, with a magnetic needle inside the housing. These are basically two instruments in one…The bit that always points North and a Protractor.
You can buy all sorts of types of compass, thumb compasses for orienteering, sighting compasses for accuracy, and electronic ones in your watch or phone., but for hill use, a standard “Silva Type” is preferable as they are simple to use.
The magnetic needle always points to magnetic north, which is usually the Red end of the needle. The south end is often white, don’t get the two mixed up as you will end up walking 180 degrees in the wrong direction, and that can and does happen, there was a group in the Cairngorms back in 2013 that did just that, a 180 degree error about 2 miles from the car park…It took them 3 days to reappear.
To complicate things a little more, there are several magnetic fields around the planet that affect the needle, so if you are travelling to say Australia, then there is a very good chance that the needle will “dip”, looking like it is completely stuck when holding the compass flat.
The better makes (Silva and Suunto for example) will produce compasses for different locations around the globe.
As you see in the picture below, there are many variations in declination (Adding/subtracting degrees from Grid North) depending on where on the planet you are, but our location (The UK) is fortunate to not have to worry too much about magnetism. I haven’t used that for a good 10 years now, but to be honest, I often just use the map alone.
"Only once have I had to use super accurate navigation (Whilst not on Assessment or during teaching), and that was in the back of Glencoe, in the dark, within an inversion, with a client. The mist was that thick I couldn’t see the ground… On open grassy slopes with steep sided ravines either side, using Compass bearings, pacing, slope aspect and dead reckoning, was the order of that day. I did actually quite enjoy the challenge, in a perverse way!!!"
What to look for…
A good quality compass will nearly always be oil filled to aid a settled bearing quickly. Air filled ones tend to take an age to settle down, which makes them hard to follow accurately when walking on a bearing. Be aware that the cheaper Chinese ones are calibrated as best they can for our part of the hemisphere, but they are likely to be up to 5 degrees wrong.. Imagine you are on a long navigation leg on Bleaklow. A 5 degree error could put you out 100m for every 1KM, so after 10KMs, you can be up to 1KM away in either direction! If 1Km takes you 20 minutes to walk, then it can take you up to an hour of messing around before you can work out which way it is to the pub you had the compass set to!
Compasses produced in Europe work best here, with Silva and Sunnto being the most well-known. These are manufactured in Sweden, so are set for our magnetic field, and are oil filled. These settle very quickly and allows for a half degree error…The baseplates do vary, depending on the end use, but a good one for general year round use is in the photo.
The base plate is long for taking accurate bearings.
Roamer scales for measuring distances.
Magnifying glass, very useful, especially if you need to wear glasses.
Luminous points on the north end of the needle and either side of the red arrow in the northing lines in the housing.
The compass is my Silva Type 4.