Hello, if you know which direction is weaker (if you have a rotationally symmetric cross section, this can only be due to differinces in supports), it can be enough to monitor the horizontal displacements in that direction. If everything is symmetric, you can not predict the buckling direction and have to monitor both horizontal directions (X and Y if I assume your column vertical axis corresponds to Z direction), and calculate the diagonal displacement from the 2 monitord components to get the max. horizontal displacement.