How were observations originally made ?
For this work , he had to coin more than a hundred Sanskrit mathematical terms " Siddhānta - sāra - kaustubha " , a translation of Ptolemy 's " Almagest " from Nasir al - Din al - Tusi 's Arabic version His original works include : ‍ " Siddhānta - samrāṭ " , which describes astronomical instruments , their design and construction , and observations .