FEM: better help messages at self weight

src/Mod/Fem/femsolver/calculix/writer.py

@@ -1099,13 +1099,14 @@ class FemInputWriterCcx(writerbase.FemInputWriter):
             f.write("** " + selwei_obj.Label + "\n")
             f.write("*DLOAD\n")
             f.write(
+                # elset, GRAV, magnitude, direction x, dir y ,dir z
                 "{},GRAV,{},{},{},{}\n"
                 .format(
                     self.ccx_eall,
-                    self.gravity,
-                    selwei_obj.Gravity_x,
-                    selwei_obj.Gravity_y,
-                    selwei_obj.Gravity_z
+                    self.gravity,  # actual magnitude of gravity vector
+                    selwei_obj.Gravity_x,  # coordinate x of normalized gravity vector
+                    selwei_obj.Gravity_y,  # y
+                    selwei_obj.Gravity_z  # z
                 )
             )
             f.write("\n")