An aircraft has reported at other than the assigned altitude. How is this indicated on the flight strip?

When an aircraft reports at an altitude that is different from the one assigned, it is indicated on the flight strip by circling the reported altitude in black. This visual cue helps controllers quickly identify discrepancies between the aircraft's actual altitude and the assigned altitude in order to ensure safety and situational awareness during operations.

The use of a black circle serves as a clear alert for controllers to take appropriate action, such as communication with the pilot or cross-referencing the altitude with radar data. The design choice of using black helps maintain a consistent and easily readable format that stands out against the other information on the flight strip.

Other visual markers, such as highlighting in yellow, underlining in blue, or marking with a red cross, may be used for different situations or indications on flight strips, but circling in black specifically denotes an altitude deviation.