Course Deviation Indicator
What is course deviation indicator?
The course deviation indicator (CDI) is a navigation instrument with a needle that moves left or right across the instrument face to show your position relative to a selected course or radial. The needle centers when you are on the chosen radial or its reciprocal, and the display includes an omnibearing selector (OBS, or course selector) to pick the course and a TO/FROM indicator. Think of it as a "fly toward the needle" guide—if the needle deflects right, your course is to the right.
Also known as: CDI, course deviation indicator, left-right needle
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