The Harmony Score is based on the deviation of the muscle score values and puts the scores into clusters.

Those clusters are:
Cluster 1 = Muscle Score between -4 and -2
Cluster 2 = Muscle Score between -1 and 1
Cluster 3 = Muscle Score between 2 and 4

If all the Scores are in one Cluster, the Harmony score will be 10. On the other hand, if the scores are spread all over the clusters, the score will be around 1.8.