adjustment ($G$) to bring them [to]{} a common flux scale with the light curve of [the]{} 5100 [Å]{} continuum [using]{} $$F_{\lambda}(5100~\text{\AA}) = \varphi F_{\lambda}(V)_{\rm obs} + G.$$ The interval for comparison is adopted to be 50 days for all the datasets. Table \[tab\_lc\] also lists the values of $\varphi$ and $G$ for all the spectroscopic and photometric datasets. In the right panels of Figure \[fig\_lc\], we plot the intercalibrated light curves of $V-$band and 5100 [Å]{} flux densities, and H$\beta$ integrated fluxes. The original light curves without intercalibration are plotted in the left panels of Figure \[fig\_lc\] for comparison. Appendix A tabulates a portion of the merged light curve of [the]{} 5100 [Å]{} and $V$-band fluxes, while the entire light curve data is available in the online journal.

The Dataset of [@Miller1979] {#sec_miller}
----------------------------

[@Miller1979] compiled the $B$-band data of Ark 120 over 1935-1950 using the archival plate collection of the Harvard College Observatory. Albeit with poor cadence and low measurement accuracy, this dataset still provides precious historical variation information of Ark 120. Indeed, [@Miller1979] detected significant flares around 1937-1939. We digitalize Figure 1 of [@Miller1979] and obtain the $B$-band magnitude data. It is impossible to intercalibrate this dataset with 