Things to do:

The tables contain observation time in hours and minutes, as well as an
exposure time.  This means a START_TIME and STOP_TIME can be calculated
for each table.

Exposure time is given in seconds, but with zero-padding (which might read
as octal).

Null values need inserting.

Fields that have at least one missing value (indicated by blanks):

  Limit flag   
  Magnitude 
  Error     
  Aperture (this field may really only be F4.1)
  Time - hours and minutes (both are either present or absent)
  Exposure time - sometimes zero-padded
  Airmass
  Chopping distance
  Chopping direction (sometimes a direction is indicated without 
    a distance)
  Beam offset (actually only F4.1)
  Offset position angle (only F5.1)
  Origin label (I1)  This is never > 1.
  Filter table number (I2)
  Comment note (A2)

All times are given to no better accuracy than 0.001 day, which is
86 seconds.  So only minutes are significant.