Long-term variations of 1A 0535+262 in log(V/R) and optical V band. Top panel: evolution of log(V/R). We use different symbols to represent the different profiles of spectral lines: stars represent the spectral profiles with V > R, triangles represent the spectral profiles with V < R. Bottom panel: long-term light curves of optical V band. We omit the legend for conciseness; it is the same as the fourth panel of Fig. 1. The vertical green lines mark the minimum brightness in the photometric V band at the V = R phase before the start of the V > R phase at ∼MJD 55850 and 56800, respectively.