Final answer:
A dot on the Horizontal Situation Indicator (HSI) represents a deviation of 2.5 degrees for an Instrument Landing System (ILS) and about 5 to 10 degrees for VHF Omnidirectional Range (VOR) navigation.
Step-by-step explanation:
The dots on a Horizontal Situation Indicator (HSI) represent the aircraft's position relative to a particular navigational path, such as that provided by an Instrument Landing System (ILS) or VHF Omnidirectional Range (VOR). A single dot corresponds to a deviation of typically 2.5 degrees left or right from the intended course for an ILS. For VOR navigation, each dot on the HSI indicates a deviation of about 5 to 10 degrees from the selected radial, varying based on the specific equipment used. Pilots use these indications to make corrections to their flight path to remain aligned with the desired navigational course.