Continuum flux density of NGC 4418 at mm wavelengths. The red diamonds represent the average value of line-free channels in the ALMA bands 3, 6, and 7. Sub-mm continuum levels from Sakamoto et al. (2010) and Sakamoto et al. (2013) are shown as blue triangles. Error bars were calculated as the quadrature sum of the spectrum rms and a calibration uncertainty of 10%. The dot-dashed, and dashed lines represent the power-law fit of data points above 200 GHz (α = 3 ± 0.6) and below 270 GHz (α = 2 ± 0.4), respectively. The red solid line shows the best fit to the ALMA baseline with a third-order polynomial. The best fit parameters are A = 2.7 × 10^-9 Jy/GHz³, B = 6.2 × 10^-8 Jy/GHz², C = 3.2 × 10^-5 Jy/GHz, D = 2.3 × 10^-3 Jy.