The Universal System of Astronomy, Part Two

The Application of the Quadrant Instrument

...and in this instrument yantra; a mechanical device used for astronomical observations, even when it is used for a period of three years original: saṃvatsaratraya; this may refer to a cycle of corrections or the durability of the instrument's calibration, a correction of sixty-five [units] is applied. Within that, the parts of the circumference paridhi; the outer boundary or perimeter of the circular scale represent the altitude original: uccatā; the angular height of a celestial body above the horizon.

In that context, following this method, the calculation is performed for the day elapsed original: dinagata; the time passed since sunrise during the northern course of the sun. It is said that this was not explicitly stated before, but now it is declared as "well-known." Indeed, in the famous Quadrant instrument tūryayantra; a specialized tool representing one-fourth of a circle, used to measure altitudes and determine time, this was not mentioned in such a way, although it is obtained through the established rules of observation.

In the accurate instrument original: spaṣṭa-yantra; likely referring to a refined or corrected version of the quadrant, this is indicated for the purpose of making the three hundred original: triśata; likely referring to 300 divisions or degrees on a specific scale divisions known. However, at the end of this work, the remaining tasks are explained. The idea is that those skilled only in logic did not understand the minute divisions of the parts; having performed these calculations, the essence should be known, as it was previously neglected. 25

This same point is clarified concisely: the various positions and divisions of all quadrants are clearly described in the Jewel of Instruments Yantracintāmaṇi; a famous 16th-century Sanskrit treatise on astronomical instruments by the scholar Cakradhara. Therefore, it should be understood that the "five centers" have been mentioned for this reason. 25

By inserting the pin kīlaka; a gnomon or central peg used to cast a shadow or act as a pivot and considering the arrangement of the frame, the parts become clear. Because of their variations and refinements, the text of the Jewel of Instruments was composed based on the principles of planetary mathematics graha-gaṇita; the branch of astronomy dealing with the mathematical tracking of planetary motions. Its essence is clear. For the sake of ease of use, in the calculation of the Quadrant instrument, one should imagine the position of the center original: kendra... having placed the line within the world...