A magnetic compass can be used to measure........
🧠Understanding Compass Measurements
A magnetic compass is a fundamental instrument in surveying used to determine the direction of a line relative to the Earth's magnetic field. Its primary functions are to establish the magnetic meridian and measure magnetic bearings.
🔬 Detailed Analysis of Terms
Magnetic Meridian
The magnetic meridian is the horizontal line at any location that represents the direction of the Earth's magnetic field. A freely suspended, properly balanced magnetic needle will align itself with this line. A compass's core function is to find this meridian, which serves as the reference direction for all subsequent measurements.
Magnetic Bearing
The magnetic bearing of a survey line is the horizontal angle that the line makes with the magnetic meridian. The compass is used to measure this angle. The two main types of compasses used in surveying are the Surveyor's compass and the Prismatic compass, which read bearings in the Quadrantal and Whole Circle systems, respectively.
Arbitrary Bearing
An arbitrary bearing is the angle a line makes with an arbitrary meridian—a reference direction chosen for convenience (e.g., pointing towards a prominent local feature). This is not measured with a magnetic compass, as the compass is specifically designed to reference the magnetic meridian.
Conclusion
Based on these definitions, a magnetic compass is used to measure both the magnetic meridian (by its needle's alignment) and the magnetic bearing of survey lines relative to that meridian. It cannot measure an arbitrary bearing.
📚 Further Reading
To learn more about the different types of surveying compasses and their specific uses, check out our detailed guide: