Quadrant & Astrolabe
The quadrant and astrolabe are instruments that go back a long time. Both have their origin in landsurvey and astronomy where they were used for measuring vertical angles. Both instruments use gravity as a reference. However, where the quadrant uses a plumb bob that slides along a scale (requiring the instrument to be held exactly vertical), the astrolabe uses an alhidade or pointer that rotates along a scale that is kept vertical by its sheer weight. All astrolabes in my collection are of the nautical type, i.e. they cannot do any elaborate astronomical computations. All instruments in my collection are either models or replicas as these instruments are very hard to find and if found are very expensive.