We report measured ferromagnetic susceptibility and our unifield model of hysteresis, physically describing hysteresis from minor to saturate loops and virgin and anhysteretic susceptibilities. Normal susceptibility for reversals, ΔM/ ΔH , and for the virgin curve, M/H, is the sum of anisotropic reversible and cooperative irreversible susceptibilities. Effective field is derived from Maxwell's thermodynamic and electromagnetic equations as the sum of Amperian, shape demagnetization, internal and external stress, eddy current and thermal fields. Rate dependence is modeled by time shifts and amplitude changes to our functions. We measure Faraday induction of ring and plate samples and vibrating sample magnetometer moments of a disc sample of mild steel, discussing procedures and precision. We find anhysteretic susceptibility to be our saturate susceptibility for positive magnetization, reflected in symmetry, with maximum susceptibility modified by each of the five fields.