Question

How did the Inca make such precise calculations in astronomy, architectural engineering, and mathematics?

Answer 1

They recorded numbers using the knots on a string called a quipu.

Answer 2

Some time ago archeologists discovered some strange strig device that was used by the Inca to make calculations.They used for solving mathematical problems as wel as for keeping records .Quipu , as it was called, was helpful in helping the Inca making very precise calculations.It was also used for administrative purposes.The chords contained numeric values and were used in engineering as well as in architectural  construction .