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Evidence is presented for a relation between the visual absolute magnitudes of SNe Ia and their minimum ejection velocities of calcium as indicated by the red edge of the Ca II H and K absorption blend in moderately late--time spectra. Independent calibrations by means of (1) the Cepheid--based distance to NGC 5253, the parent galaxy of SN 1972E, and (2) light--curve calculations based on hydrodynamic models of SNe Ia, give $\rm H_0 \simeq 55 \pm 10\ km\ s^{-1} \ Mpc^{-1}$. We estimate the distance to NGC 4536 and its SN 1981B to be $19 \pm 3$ Mpc. A Cepheid--based distance to NGC 4536 is expected to be available in the near future.
