Optical device for vertically positioning a sextant

摘要

An optical device for vertically positioning a sextant to minimize the "tilt error" which occurs in a measured angle of altitude whenever the sextant is not held orthogonal to the horizon. The optical device can be fixed to the sextant and provides in the sextant's viewing area a secondary horizon which will align with the direct horizon only when the sextant is in a vertical orientation. The device is capable of periodic calibration and can be pivoted out of the line of sight when the sextant's user is initially locating the celestial body whose altitude is being measured.