the external data set must have the following form
record 1:  title  (a80)
record 2:  information describing the table
columns
1-32  format of data entries  (a32)
33-34  not used
36-42  julian day of first value in table  (i7)
44-50  julian day of last value in table  (i7)
52-53  maximum number of pairs of values per record  (i2)
55-56  interval in days betweeen tabular values  (i2)
58-72  units of values in arcseconds  (e15.7)
records 3-end:  data entries - format is read in record 2, but
must be of the form integer mjd folowed by up
to 6 pairs of integer values of xwob and ywob.
if a record is short, the number of pairs of
values in that record is given in columns 79-80.