JP 3-50 National Search and Rescue Manual Vol I - US Navy

Figure 6-10. Sun Position and Target Detectability
4. A geometric scanning pattern should be used routinely when
searching. Ideally, the eyes should move and pause for each 3
degrees or 4 degrees of lateral and/or vertical distance at a
rate that will cover about 10 degrees per second. A sighting
is most likely to occur in an area limited by a 5 degrees
radius in all directions from the point at which the eyes are
focused. Scanners should not jump their eyes between
fixations and should pause only briefly between fixations
during daylight search. Poor scan patterns consist of
prolonging fixations in a single area, allowing the eyes to
jump around, or scanning along structures like window frames
or environmental features within the field of view. When
searching in areas of little contrast, eyes tend to focus
short of the surface being searched. To preclude this, the
scanner should periodically focus on some object in the "no
contrast" area, or on a nearby object within or on the SRU.