Bharatiya Jyotihshastra (History of Indian Astronomy), translated by R. V. Vaidya v2.c12.s3.34

v2.c12.s3.34

On this basis, the different values of yojana, mentioned by Hiouen Thsang come to 8⅙, 6⅛, and 3⅓ miles. In other words, the measure of a yojana according to current practice in his time was 6⅛ miles. General Cunningham also compared the distances between several well-known places, given by Hiouen Thsang, with the actual ones, and decided that Hiouen Thsang's 6 Li were equal to one mile.* But the distances given by Hiouen are those along roads by which he actually travelled; and the roads and paths are not always in a straight direction. Hence, in Cunningham's opinion, in order to get the direct distance between two places, distance given by Hiouen Thsang should be reduced by ⅙ and Cunningham has done so at several places; and if this rule be followed, the distance of 6 Li given by Hiouen is equal to (6-1=5) Li in a straight direction; and thus, the measures given by Cunningham and St. Martin agree with one another. On the whole, the author feels that the unit of yojana equal to 30 Li was in use in Hiouen's time, and that while converting his distances into miles, six Li must be assumed to be equal to one mile; in other words, according to the then prevalent system, one yojana was equal to 5 miles. And the diameter of the earth, 1581 yojanas, mentioned by Brahmagupta who lived just before or about the date when Hiouen came to this country in the 7th century A.D., comes to 7905 miles; and this figure is very nearly equal to that of the accurately established modern measure of the diameter.