The vertical level consists of a glas prism, which can be mounted subsequently.
In case of tilting the sextant the horizon that is visible through the prism is not in line with the real horizon.
Error by tilting of the sextant
This error is approximate 7nm at a tilt of 5° and a star height of 45°.
1) To avoid this, the sextant was previously swivelled around the
2) The vertical reference is a glass prism. When the sextant is tilted,
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