Cross-staff, Navigational Instrument

Colorized illustration of the cross-staff, or fore-staff. This navigational instrument is composed of a square staff and three vanes of different lengths. The sides of the staff have different scales, each corresponding to one of the vanes. When observing the altitude of the sun only one vane is used. Holding one end of the staff to his eye, the observer moves vane until he sees its lower end level within the horizon and the upper end in one with the sun. The altitude is read off where the cane cuts the staff

Restrictions Only for Ireland and United Kingdom

Cross-staff Diagram Fore Measure Navigators Perpendicular Sliding Vane

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