The correct answer is D. presence of magnetic substances near the instrument.
Local attraction is a phenomenon that occurs when a compass needle is affected by the presence of magnetic substances near the instrument. This can cause the needle to point in a different direction than it would if there were no magnetic substances present.
There are a number of things that can cause local attraction, including:
- The presence of iron ore in the ground
- The presence of electrical wires or cables
- The presence of other magnetic instruments
If you are experiencing local attraction, there are a few things you can do to try to correct it:
- Move the compass away from any magnetic substances.
- Use a compass that is designed to be resistant to local attraction.
- Use a compass that is calibrated for the area you are in.
If you are still experiencing local attraction after taking these steps, you may need to consult with a professional surveyor.