r.king      march 1978      subroutine eatzdl
calculate the theoretical zenith delay of the earth's
atmosphere using input meterological data or monthly
average values for the observing site(s)

read in meterological data from save vector
units of temp, pressure, and relative humidity are deg kelvin,
millibar, and fraction of unity
if there are no values for the pressure and temperature on the
obslib tape,dummy values must be made up