  Ru{\dj}er Bo\v{s}kovi\'c developed methods for determination of solar
rotation elements: the solar equator inclination i, the longitude of the node
{\Omega} and the period of solar rotation. In his last work Opera pertinentia
ad opticam et astronomiam, published in 1785, in the chapter Opuscule II he
described his methods, the formulae with figure descriptions and an example for
calculation of the solar rotation elements with detailed numerical explanation
using his own observations performed in September 1777. The original numerical
procedure was performed using logarithmic formulae. In present work we give a
description of the original results of R. Bo\v{s}kovi\'c and compare them with
our recalculated values.
