The compass course has added the magnetic deviation and the magnetic variation to the true course . The difference between the reading of a compass and the actual magnetic course or bearing due to errors in the compass reading. These errors can be caused by metals, magnetic fields and electrical fields near the compass. Prior to using a compass, magnetic deviation should be recorded for many different points on the compass as the error can be different at different points. The act of checking for magnetic deviation is called swinging .
Charts usually have more that one compass rose.
In that case the compass rose nearest to the object being plotted should be used as the geographic directions and magnetic variations may change slightly in different places on the chart. A device used to draw circles. An object made with more than one type of material. A type of compressed gas used as fuel for stoves and heaters. CNG is stored in metal cylinders prior to use.