Distribution of the phase-averaged magnetic field strength B₀ for the long-period Ap stars of Tables 1–3 of this paper, of Table 1 of Paper I and of Table A.1 of Paper II. The orange and red parts of the histogram correspond to the stars for which measurements of the mean magnetic field modulus or of the mean quadratic magnetic field are available; for the remaining stars (blue part of the histogram), a lower limit of B₀ was inferred from the existing mean longitudinal magnetic field measurements. Orange distinguishes the known ssrAp stars that were not identified as ssrAp star candidates on the basis of our TESS-based photometric survey.