slit Ratio error -1 18.64 0.4 -2 18.18 0.38 -3 20.85 0.5 -4 18.15 0.34 -5 17.44 0.31 -6 17.38 0.32 -7 17.82 0.32 -8 16.41 0.27 -9 18.51 0.37