<P> The deflection of the needle is proportional to the course deviation, but sensitivity and deflection vary depending on the system being used: </P> <Ul> <Li> When used with a VOR or VORTAC, the instrument can be referred to as an "omni bearing indicator" ("OBI"). The courseline is selected by turning an "omni bearing selector" or "OBS" knob usually located in the lower left of the indicator . It then shows the number of degrees deviation between the aircraft's current position and the "radial" line emanating from the signal source at the given bearing . This can be used to find and follow the desired radial . Deflection is 10 ° deviation at full scale (each side), with each dot on the CDI representing 2 ° . (See Using a VOR for usage during flight .) </Li> <Li> When used with a GPS, or other RNAV equipment, it shows actual distance left or right of the programmed courseline . Sensitivity is usually programmable or automatically switched, but 5 nautical miles (9.3 km) deviation at full scale is typical for en route operations . Approach and terminal operations have a higher sensitivity up to frequently . 3 nautical miles (0.56 km) at full scale . In this mode, the OBS knob may or may not have an effect, depending on configuration . </Li> <Li> When used for instrument approaches using a LDA or ILS the OBS knob has no function because the courseline is usually the runway heading, and is determined by the ground transmitter . A CDI might incorporate a horizontal needle to provide vertical guidance when used with a precision ILS approach where the glideslope is broadcast by another transmitter located on the ground . </Li> </Ul> <Li> When used with a VOR or VORTAC, the instrument can be referred to as an "omni bearing indicator" ("OBI"). The courseline is selected by turning an "omni bearing selector" or "OBS" knob usually located in the lower left of the indicator . It then shows the number of degrees deviation between the aircraft's current position and the "radial" line emanating from the signal source at the given bearing . This can be used to find and follow the desired radial . Deflection is 10 ° deviation at full scale (each side), with each dot on the CDI representing 2 ° . (See Using a VOR for usage during flight .) </Li> <Li> When used with a GPS, or other RNAV equipment, it shows actual distance left or right of the programmed courseline . Sensitivity is usually programmable or automatically switched, but 5 nautical miles (9.3 km) deviation at full scale is typical for en route operations . Approach and terminal operations have a higher sensitivity up to frequently . 3 nautical miles (0.56 km) at full scale . In this mode, the OBS knob may or may not have an effect, depending on configuration . </Li>

When is the course deviation indicator (cdi) considered to have a full-scale deflection
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