Hilchos Kiddush HaChodesh 13:1
In order to determine the actual position of the sun on any given day, one must first calculate its average position using the methods described until this point. Next, one calculates the position of the sun’s apogee. After doing so, subtract the apogee from the sun’s average position. What remains is called the sun’s course.
Hilchos Kiddush HaChodesh 13:2
The angle of the sun’s course is calculated as follows: if the sun’s course is smaller than 180 degrees, subtract it from its average position; if it is greater than 180 degrees, add it to the sun’s average position. The number resulting from this addition or subtraction is the sun’s actual position.