page_title: Octant (instrument)
section_title: Advantages of the octant
hierarchical_section_title: Octant (instrument) / Advantages of the octant
caption_attribution_description: Photo of octant details. Reverse side of octant showing some brass components and the ivory notepad.
context_page_description: The octant, also called reflecting quadrant, is a measuring instrument used primarily in navigation. It is a type of reflecting instrument.
context_section_description: The octant provided a number of advantages over previous instruments.
  The sight was easy to align because the horizon and the star seem to move together as the ship pitched and rolled. This also created a situation where the error in observation was less dependent on the observer, as he could directly see both objects at once.
  With the use of the manufacturing techniques available in the 18th century, the instruments were capable of reading very accurately.  The size of the instruments was reduced with no loss of accuracy.  An octant could be half the size of a Davis quadrant with no increase in error.
  Using shades over the light paths, one could observe the sun directly, while moving the shades out of the light path allowed the navigator to observe faint stars.  This made the instrument usable both night and day.
  By 1780, the octant and sextant had almost completely displaced all previous navigational instruments.
caption: Octant reverse side. This side is not seen in photographs very often. On the right, the thumbscrew to adjust the horizon mirror can be seen. At the top, one of the feet on which the octant rests in its case is just below the index arm axis. On the left the notepad is clearly visible. This small keystone-shaped piece of ivory, scarcely larger than a thumbnail, was used by the navigator to record his readings.
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