Which of the following instruments uses magnetic fields for directional reference?

The magnetic compass uses magnetic fields for directional reference by aligning itself with the Earth's magnetic field. It consists of a magnetic needle that pivots freely and points toward magnetic north. This instrument is fundamental in navigation, allowing pilots and mariners to determine their heading relative to the Earth's magnetic poles. The ability of the compass to react to magnetic fields makes it a reliable tool for direction-finding, especially in environments where GPS signals may not be available or reliable.

The other instruments mentioned either do not utilize magnetic fields or serve different purposes. The gyroscopic compass, for example, relies on the principles of gyroscopic motion rather than magnetism. An accelerometer measures changes in velocity or acceleration, and an inclinometer is used to measure angles of slope or tilt, neither of which depends on magnetic fields for their functionality.