seven-thirds rule

seven-thirds rule

[¦sev·ən ′thərdz ‚rül] (navigation) A thumb rule which states that the approximate distance to an object broad on the beam equals seven-thirds of the distance traveled by a craft while the relative bearing (right or left) changes from 22.5° to 26.5°, 67.5° to 90°, 90° to 112.5°, or 153.5° to 157.5°, neglecting current and wind.