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When the solver opens, click on to open the Mesh menu in the menu bar. In the Details window, expand Sizing, and change the Element Size from Default
to 0.5 m
(Make sure the units are set to meters by selecting Units > Metric(m, kg, N, s, V, A) in the menu bar)
Generate the Mesh
When the sizing has been specified, press Mesh > Generate Mesh to create the mesh.