Her X-1 long-term light curve, showing the maximum flux of each 35 d cycle in units of ASM-cts/s, as determined from observations by the monitoring instruments: red points are from RXTE/ASM, blue points are from Swift/BAT. Measured BAT values (in units of cts/(cm² s)) were scaled to ASM-cts/s using the scaling factor determined from the overlapping time period (MJD 53 433–55 248). For better readability of the light curve, only a few error bars are shown. Three anomalous lows (Coburn et al. 2000) can be recognized (indicated by AL). The rather low flux value of the latest NuSTAR observation is also marked (NuSTAR 15). The solid line is a linear fit to the data (excluding those points belonging to the ALs). Its slope is −(1.30 ± 0.09) × 10^-4 (ASM-cts/s)/d, which corresponds to a small reduction in flux of (0.95 ± 0.07) ASM-cts/s over 20 yr.