ZHD0 is computed at sea level from P0 = SLP using the modified Saastamoinen model (Davis et al., 1985, Eq (5), Section 3.1). To compute the corresponding value at station height, ZHDs, the pressure at station height, Ps, is first computed from SLP using Eq. (8) and then ZHDs is computed from Ps using again Eq. (6).