The impedance file determines both the number of bins and the bin width: with Nf points spaced by Δf, the element uses Nb = 2(Nf - 1) bins of width 1∕(NbΔf). The N_BINS and BIN_SIZE parameters from ZLONGIT/ZTRANSVERSE are present for compatibility but are overridden by the file. Bins are centered as in ZTRANSVERSE (bin centers at tmin + idt); the AREA_WEIGHT option is honored on the longitudinal current histogram only.