Before revision: The iron made surveying instruments such as metric chains, ranging rods and arrows should also kept at a safe distance apart from compass.surveying by Prof. Cl Kocher Detection Local attraction at a place can be detected by observing bearings from both ends of the line in the area.
After revision: beThe iron made surveying instruments such as metric chains, ranging rods and arrows should also kept at a safe distance apart from compass.surveying by Prof. Cl Kocher Detection Local attraction at a place can be detected by observing bearings from both ends of the line in the area.