Compass surveying – magnetism basics: Which statements about magnetic meridian, magnetic variation (declination), dip, and balancing a magnetic needle are correct?

Introduction / Context:
Compass work relies on Earth’s magnetic field. To interpret bearings correctly, a surveyor must know how a magnetic needle behaves, how magnetic meridian differs from the true meridian, and how instruments compensate for dip and balance. This question validates those fundamentals.

Given Data / Assumptions:

• A freely suspended magnet aligns with the horizontal component of Earth’s magnetic field.
• True and magnetic meridians generally do not coincide.
• The Earth’s field is inclined to the horizontal, producing dip.
• Compass needles are adjusted for balance and sensitivity.

Concept / Approach:
The magnetic needle seeks the magnetic meridian. The angle it makes from the true meridian is the magnetic declination (variation). Because the field is inclined, the needle experiences dip toward the nearer magnetic pole; counterweights or rider weights are used to balance the needle on its pivot for smooth motion without rubbing the glass cover.

Step-by-Step Solution:

Verification / Alternative check:
Standard compass descriptions include declination adjustment scales and rider weights for balancing; dip is handled by needle design and counterbalancing for local latitude.

Why Other Options Are Wrong:

• Selecting only one statement ignores other fundamental behaviors; all are simultaneously true in normal surveying practice.

Common Pitfalls:
Assuming magnetic and true meridians coincide; ignoring time-varying declination; neglecting to balance the needle after moving instruments across latitudes.

Final Answer:
All of the above