MR_ArPdGet
pd = MR_ArPdGet(arRef, physArm, map);
pd = MR_ArPdGet(arRef, physArm + 1, map);
pd = MR_ArPdGet(arRef, 0, map); /* Get the Pd. */
pd = MR_ArPdGet(arRef, 1, map); /* Get the Pd. */