The central portion of the face was occupied by a larger circle, half-green and half-black; the former portion representing the colour of the daylight sky, the latter emblematic of night.

On this circle the Sun and the planets were represented by figures whose movement showed exactly the actual place of each in the celestial sphere.

The two Moons were also figured, their phases and position at each moment being accurately presented to the eye.

Around this circle was a narrow band divided into strips of different length of various colours, each representing one of the peculiar divisions of the Martial day; that point which came under the golden indicator showing the _zyda_ and the exact moment of the _zyda_, while the movement of the inner circle fixed with equal accuracy the period of day or night.

Below were other circles from which the observer could learn the amount of moisture in the atmosphere, the intensity of the sunlight, and the electric tension at the moment.