Hi, I would like to calculate the inertias of two articulated bodies. First, I created a floating body in the XML with a diaginertia. When I tried to the inertia information from mjData->cinert with one body, it gives me diagonal inertia as I inputted. However, when I created two linked bodies in the XML with the diaginertia, I can't get the diagonal information from mjData->cinert. My testing model is attached below. And I tried to read by, for (int i = 0; i < 2; i++) { for (int j = 0; j < 3; j++) for (int k = 0; k < 3; k++) _inertia_CoM_mjc[j][k] = mjData->cinert[i*10 + j * 3 + k]; } It seems that mjData->cinert gives diagonal elements in the first three components when I tried with one body. However, I'm not sure that with two bodies. How can you calculate the inertias of linked bodies? And in what order does mjData->cinert give? Thank you.