Final answer:
Variation and deviation are terms used in a magnetic compass to describe errors or discrepancies in compass readings. Variation refers to the angular difference between true north and magnetic north caused by the misalignment of the Earth's magnetic field. Deviation refers to errors in compass readings caused by local magnetic fields or metallic objects.
Step-by-step explanation:
In the context of a magnetic compass, the terms variation and deviation are used to describe the errors or discrepancies in the compass readings.
- Variation refers to the angular difference between true north (geographic north) and magnetic north. This variation occurs because the Earth's magnetic field is not perfectly aligned with its geographical axis. The variation can be different at different locations on Earth and may change over time.
- To compensate for variation, navigational charts provide information about the local variation for accurate compass readings.
- Deviation refers to the errors in compass readings caused by local magnetic fields or metallic objects on the boat or aircraft. These external magnetic fields can cause the compass needle to be deflected from its true magnetic heading.
- Deviation is unique to each vessel or aircraft and can be determined by calibrating the compass with known headings in the presence of the vessel's or aircraft's magnetic environment. Deviation can be corrected using deviation cards or corrections, often provided in a compass correction table.