Relationship between the true (3D) radial velocity and observable (projected) line-of-sight velocity. Colors represent mass fraction (top), mean temperature (middle), and mean metallicity (bottom). Here we stack all TNG-Cluster halos and use all gas cells together, giving equal weights to individual halos. In the top panel only, each column is normalized such that the sum equals unity. It is not possible to infer the inflowing (negative radial velocity) versus outflowing (positive radial velocity) gas solely from its line of sight velocity. However, strong correlations are evident between velocity and temperature which can help break the degeneracy.