Abstract: A mechanical calculating device is provided which is particularly useful in determining the relationship of the heavenly bodies to specific heavenly positions at different times. The device, in the embodiment to be designed, comprises a base, a first disc rotatably mounted on the base, which has inscribed about its periphery a ring scale divided into twelve sectors each marked with a different Zodiacal sign, and each sector is subdivided into thirty indices each representing one degree of arc. A plurality of transparent discs are rotatably mounted on the base in concentric relationship with one another and with the first disc, the latter discs representing the sun, the moon and the various planets. The latter discs are each provided with an identifying tab, and each is inscribed with a series of lines extending outwardly from a common point adjacent to the tab at selected angles to one another, with each line having a selected color.