Übersetzen...
Automatische Übersetzung:
The term cross-staff, also Jacob's staff, ballastella, balestilha, or fore-staff is used to refer to several things. The two most frequent uses are: in astronomy and navigation for a simple device to measure angles, and in surveying for a vertical rod that penetrates the ground and supports a compass or other instrument. The cross-staff consisted of a long staff with a perpendicular vane which slides back and forth upon it. The staff is marked with graduated measurements - calculated by trigonometry. The angles can then be measured by holding it so the ends of the vane are level with the points to be measured. Early in the sixteenth century it was already in use as a seaman's navigational instrument.