Everyone knows what is a compass, but do you know that the compass is not pointing the True North, instead it is pointing the Magnetic North which is constantly changing. Here is an article by by NGO indicating the the magnetic north is moving toward Russia.
A normal compass will only give you a guided direction however it cannot be use on a Topographic or Hiking Maps. Topo maps use True North so you will need a hiking compass to go with it. Depending which part of the world your are in, Declination and Inclination are used on Topo Maps and on the hiking compass. It is the difference between True and Magnetic North. The vid below will explain in details.
You can check online calculator that shows you the Declination on the particular location.
If you planning to get a compass, a simple base plate compass is commonly use with Topo Maps. It should have all these features as shown above. Do take note on the scale Units on the compass, if you are using a metrics map thats means it shows meters or Kilometers you will need a compass with these units. The pic above is an imperial units compass which is using Miles. Some compass do come in both units. You should also get a base plate compass that is transparent so you can see the map below it.
A Lensatic Compass is currently use by the military, it is the same as normal hiking compass expect it has a sight and magnifying lens to give you the precise bearing. Simply look through the sight at the direction of the object such as tower or mountain and turn the dial to the needle pointing north. This is a precise "Sight n Go" which is rather easy to use. However military lensatic compass are of better quality and they do not come cheap.
Foldable Base Plate Lensatic Compass
