Hi Yeukai! It combines the outer most path with the one before it. So if you have a data structure of {A;B;C;D} and you shift this data tree with -1 (the default), you get {A;B;C}, Merging all the items in Branch D to become branch C. I would advise you to watch the Grasshopper 101 and Grasshopper 102 for a more broader explanation. https://thinkparametric.com/courses/grasshopper-101-introduction-to-parametric-modelling https://thinkparametric.com/courses/grasshopper-102-data-lists-and-tree-structures Especially the Data Trees part on both. Cheers! Arie