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« Astronomiae Instauratae Mechanica » - QUADRANS MEDIOCRIS  i
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i  « ... The quadrants were called so because they could rotate about the "alidade": the rotation was equivalent to 90° ... the pictured one is a "brass mean azimuth quadrant" ... and it also was the last instrument Tycho ordered outside ... afterwards, he manufactured everything in his own workshop, with great advantage for the quality control. This also allowed to improve procedures very much... all his studies helped him to build the colossal "mural quadrant" having a radius of 2 m. ...  »  i
«… With the use of a plumb-line "G", the instrument was leveled, so that its horizontal circle would become parallel to the local horizon …  i  The "pre-requisite" required a reasonable estimate of the position of a "star" or of an "errant star" , otherwise, called planet …  i  The instrument was positioned towards where the star was expected to rise. Once it appeared in the view-finder, the star could then be perfectly locked ...  i  Horizontally, the instrument could be rotated: 360° ...  i  Vertically, the instrument ranged from 0° to 90° ... therefore, it could be directed towards any point of the celestial vault ...  i  "The same measurement was repeated many times by different assistants", each of them used a different instrument. In this way it was possible to statistically improve the accurateness of the measurement, for example by using a "mean value" ... »  i
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« Astronomiae Instauratae Mechanica » - QUADRANS MURALIS  i
«… This is considered Tycho’s masterpiece, the very famous mural quadrant with a radius of 2 m. ...  z  It was fixed to a wall oriented towards the North-Southern meridian ...  z  As per figure below: the view-finder had two narrow openings in line with a cylinder having same measures... the star must show the same brilliancy, while observing a ray and, immediately after, the second one ...  i