Powered by the then-new double barrel Cal. 94900, the Sidérale Scafusia focuses on astronomical complications above all others. It features a tourbillon and perpetual calendar, but these are incidental to the main function. In fact, the calendar only displays the leap year and numbered day of the year, not the month, day, or date.
The primary function of the Sidérale Scafusia is calculation of sidereal time and a celestial calendar. Sidereal time is shown on the face in a sub-dial at 12 00 using a two-handed 24-hour display. The reverse side features the perpetual calendar and signature celestial map. The astrological chart is only accurate to a customer-chosen position on earth, but IWC claims it can accurately show the position of over 500 stars from there. It also displays sunrise and sunset time at that location.