What is the reason for "swinging" a compass?

"Swinging" a compass is performed primarily to compensate for deviations caused by magnetic fields. This process involves adjusting the compass to ensure that it accurately reflects the aircraft's heading, regardless of the interference from various magnetic sources within the aircraft itself.

As the aircraft contains numerous components that generate magnetic fields—such as electrical equipment, metal structures, and even the earth's magnetic influence—these can cause inaccuracies in the compass reading. During the swinging process, the compass is taken to a location away from magnetic interference, and the readings are compared to known bearings. This allows for adjustments to be made to eliminate these deviations, ensuring the compass provides an accurate heading while the aircraft is in flight.

The other options do not relate directly to the purpose of swinging a compass. Balancing weights inside the compass is not standard practice, as the compass is designed to operate with a specific mass distribution. Increasing sensitivity is not a function of this process either, as the sensitivity of the compass is determined by its design and materials. Recalibrating altitude readings is unrelated, as the compass does not measure altitude; it measures direction.

Thus, the primary reason for swinging a compass is indeed to compensate for those deviations that can affect its accuracy.