I want to calculate a model mass center displacement, So I use the history output "UC1","UC2","UC3". At first I use a cube to try(100mm cubelength,10 mm mesh size, CTE 1e-4, temperature load 100K， with fixed boundary condition)， so the mass center displacement is obviously 0.5 0.5 0.5. Then I want to minus the displacement at the boundary condition, so I give a (-0.5,-0.5,-0.5) boundary condition (just move the position at the boundary, not in assembly, it can expand freely), in this case, the cube can expand based on its mass center, so the mass center displacement shoule be zero, but in my model, they are(1.55175961598537e-13,1.59963893259923e-13,-1.76347705969221e-13). Yes, they are close to zero, but where the float error come from. How abaqus calculate mass center displacement. In fact I know the mesh node coordinate is saved in single accruacy, but data like 10,10.5 is accruate in single accruacy, So where is the small error comes from? Thanks for your advice