playing nine holes twice
If the same nine is played back-to-back on a course for infrequent reasons, such as course maintenance, it is acceptable to post two separate 9-hole scores resulting in two 18-hole Score Differentials. It is also acceptable and more indicative how you played, to use manual entry as long as the course played is first selected within the GHIN mobile app. Just double the rating and use the slope value as is. As an example, if the Front 9 with a Course Rating and Slope Rating of 35.1/124 is played twice, then Ratings of 70.2/124 may be used to post an 18-hole score.
If playing the same nine back-to-back is a common scenario, the course should contact the OGA to provide an 18-hole Course Rating and Slope Rating.