A Yantra with a sacred string of copper wire

Remembering that "Yantra" means, in essence, 'diagram of a machine", one can consider the Digansa Yantra. In the middle of the instrument a low pillar, about one meter in height. While the second circular wall is just like a ring, which has a same height as that of the pillar. The outermost circle, two metres height, and eight metres in diameter. On the horizons of all these circles graduated marble slabs from 0 degree to 360 degree are placed. They are even sub-divided in terms of decimal etc. Two copper wires are tightly streched ascross the exterior wall, from 0 degree to 360 degree are placed. They are even sub-divided in terms of decimals. Two copper wires are tightly streched ascross the exterior wall, from 0 degree to 180 degree and 90 degree to 360 degree, to represent the North-south and East-West directions respectively. At the center a metallic ring is tied, supported by these two strings.

The sacred pillar and thread: To determine the azimuth of the sun, the user takes a thread and fixed it from the knob of the innermost pillar's center. As the sun rises higher, the shadow of the circular metallic ring enchants its shadow on the second circular ring. We take this thread unto the outer-most circular wall graduation, through the shadow of the ring. Thus the reading of the horizon on the third wall provides the azimuth of the sun. This enables a calculation of the rise and set of the sun, over time. . See the picture here
"A full-moon day of the year is observed by those who wear the sacred thread (typically brahmins and followers of Arya Samaj) More a day of spiritual renewal and the thread was ritually replaced by new one". Arya Samaj (Arya Society or Society of Nobles) is a Hindu reform movement in India that was founded by Swami Dayananda in 1875. He was a sannyasi (renouncer) who believed in the infallible authority of the Vedas. Dayananda advocated the doctrine of karma and reincarnation, and emphasised the ideals of brahmacharya (chastity) and sanyasa (renunciation). The society was united with the Theosophical Society for a certain time, under the name Theosophical Society of the Arya Samaj.Dayananda rejected all non-Vedic beliefs altogether. Hence the Arya Samaj unequivocally condemned iconolatry, animal sacrifices, ancestor worship, pilgrimages, priestcraft, offerings made in temples, the caste system, untouchability and child marriages, on the grounds that all these lacked Vedic sanction. It aimed to be a universal church based on the authority of the Vedas. Dayananda stated that he wanted ‘to make the whole world Arya’. That is, he wanted to develop a missionary Hinduism based on the universality of the Vedas.