CASSENS & PLATH BOBBY SCHENK Sextant Handhabung Seite 25

Instructions
BOBBY SCHENK Sextant
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Terrestial or Horizontal Angle Observations
This measurement can be used to find a position near to the coast.
Swing out all shade glasses and set the alidade to zero. When the instrument is held horizontally,
the right-hand object will be sighted first. One can see simultaneously the directly seen (through
the horizon mirror) and the doubly reflected (reflected by horizon and index mirror) picture. Move
the alidade forward. Simultaneously turn yourself to the left and keep the doubly reflected picture
in view. The second left object will appear from left and can be brought exactly in line with the first
right-hand object.
Reading of angle will be carried out same as described above. In the literature you will find
descriptions how to find your position with one or two angles measured as above.
Range Finding
The distance to a terrestial object of known height can be calculated by measuring the apparent
height with a sextant. The nearer the object the higher will be the apparent angle between top and
bottom. One has to distinguish between objects in front of or behind the visual horizon. The
relevant formulae will be found in the nautical literature.
There are special sextant-like instruments called stadimeters with an expanded scale for small
angles especially for this application.