The Firmamentum is a unique measurement and navigation instrument. Fully in the tradition of the historic watches used for observation, it not only shows the Earth’s rotation through the classic measurement of time, but with the aid of the hour angle it measures the Earth’s rotation around its own axis and the visible movement of the sun, planets and stars in the heavens.

The hour angle defines a full rotation of the Earth on its own axis as being 360 degrees of angular movement. It therefore measures the movement of the Earth not in the classic sense as a unit of time, but rather it defines it in degrees. The hour angle expresses 4 minutes of our time as one
degree and 60 minutes as 15 degrees. Due to this division into degrees, navigators can determine their own position on Earth with the help of the hour angle and the visible movement of the sun, planets and stars in the sky.
In order to directly display the speed of the stars - the so-called sidereal time - which is slightly different from the bodies in our solar system, Firmamentum has integrated into it a special mechanism for the direct and exact display of one’s own position with the aid of a heavenly body outside our solar system. It therefore not only shows the solar hour angle, but also the sidereal hour angle in a second display designed to be variable. This second display of sidereal time thus permits Firmamentum to be used for the observation of a heavenly body within our solar system at the same time as the observation of a star outside our solar system. Due to a unique mechanism with a variable-speed gear train, this second display has been designed so that it can switch to the measurement of the regular solar time by means of a pushbutton at the two o’clock position. In this measurement variant, the solar hour angle and the solar time are also directly displayed, therefore making possible the simultaneous observation of two heavenly bodies within our solar system. At the same time, the solar time shown on this variable display can also be set to read regular time and therefore makes Firmamentum, which has been designed to be a true measuring instrument, into a completely normal watch with hour and minute hands if so desired.