About Lesson
Local Attraction
- Local attraction refers to the disturbance of a magnetic needle caused by nearby materials like steel structures, iron ore deposits, or electric transmission lines.
- These materials can deflect the needle, causing it to deviate from pointing directly toward Earth’s magnetic poles, thus affecting the accuracy of the magnetic bearing.
Detection of Local Attraction
- To detect local attraction at a station, compare the fore bearing and back bearing of a line:
- If the difference between the fore bearing and back bearing is exactly 180° (with no observational or instrumental errors), there is no local attraction.
- If the difference is not 180°, local attraction is present at one or both stations.