Evolution of the CWsin and ⟨|f_i|⟩ during 00:00 UT to 20:00 UT on 2014 November 7, shown in the top panel. CWsin and ⟨|f_i|⟩ are metrics to measure the quality of force-freeness and divergence-freeness of a NLFFF extrapolation. The black and red dashed lines are average values of the CWsin and ⟨|f_i|⟩, respectively. Middle panel: Distributions of the E_∇ × B and E_{∇ ⋅ B} during 00:00 UT to 20:00 UT. These two quantities can also be used to measure the force-freeness and divergence-freeness of the extrapolated fields. The black and red dashed lines show the average values of these two metrics, respectively. Bottom panel: Evolution of the free energy. Black and blue lines show the free energy calculated with different ways, the red solid line shows their relative error, and the red dashed line shows the average of the relative error. See the text for details.