The symmetric division deg index (or simply sdd-index) was proposed by Vukičević et al. as a remarkable predictor of total surface area of polychlorobiphenyls. It is one of discrete Adriatic indices that showed good predictive properties on the testing sets provided by International Academy of Mathematical Chemistry. In this paper, we investigate some properties of this graph invariant in terms of orbit structure of a graph and then we explore new bounds for sdd-index. In continuing, the inverse symmetric division deg index is defined and new results concerning these two graph indices are stablished. Finally, some bounds for both indices are presented.

对称除法度索引（或简称为sdd -index）由Vukičević等人提出。可以预测聚氯联苯的总表面积。它是离散的亚得里亚海指数之一，在国际数学化学学院提供的测试仪上显示出良好的预测性能。在本文中，我们根据图的轨道结构研究了该图不变性的一些性质，然后探索了sdd -index的新界限。接下来，定义逆对称除法度索引，并确定有关这两个图索引的新结果。最后，给出了两个指标的界限。