Which of the following is NOT a magnetic compass error?

Magnetic drift is the correct choice as it is not typically classified as a compass error. In the context of navigation and compass use, the term "magnetic drift" refers to the displacement of the magnetic north pole over time, which affects the magnetic compass's calibration. This is a gradual change on a geological timescale rather than an immediate error encountered during navigation.

In contrast, the other terms refer specifically to errors that can affect compass readings in real-time. Variation, also known as magnetic declination, is the angle difference between true north and magnetic north, which can lead to systematic navigational errors based on geographic location. Oscillation can occur due to the natural movement of a vessel or external influences, causing the compass needle to swing. Deviation, on the other hand, is an error introduced by local magnetic fields, often caused by metallic objects or electronic devices near the compass. Each of these errors can affect a navigator's ability to accurately determine direction, which is why they are important considerations in the use of magnetic compasses.