;+
; NAME:
;  rd_1_slitoffset
; PURPOSE: (one line)
;  Read a table of slit offsets
; DESCRIPTION:
;  Read a table of slit offsets
;  as written by wr_1_slitoffset
;  tables/YYMMDD_1_slitoffset.txt
; CATEGORY:
;  NIRES reduction
; CALLING SEQUENCE:
;  wr_1_slitoffset, datestr, framenum, object, airmass, slitoffset, slitoffset_override
; INPUTS:
;   datestr: string (YYMMDD)
;   framenum: array of integers.  FRAMENUM from header
;   object: array of strings. OBJECT from header
;   airmass: array of floats. AIRMASS from header
;   slitoffset: offset to the slit as used by NSX, for each exposure,
;   as calculated by nsxng_wide_profile_mash
;   slitoffset_override: override to slitoffset
; OUTPUTS:
;  none
; SIDE EFFECTS:
; RESTRICTIONS:
;  None
; PROCEDURE:
;  wrapper for nsx proceedure nsxng_wide_profile_mash
; MODIFICATION HISTORY:
;  Written 2021 Dec 30, by Leslie Young, SwRI
;-
function rd_1_slitoffset, datestr, framenum, object, airmass, slitoffset, slitoffset_override

  fn = 'tables/'+datestr+'_1_slitoffset.txt'
  if not isfile(fn) then return, -1

  format = '(A6, X,  A4, A12, A8,   A16,   A21)'

  readfmt, fn, format, date, framenum, object, airmass, slitoffset, slitoffset_override, $
           /skip, /silent
  n = n_elements(framenum)
  if n ne (file_lines(fn)-1) then return, -1
  return, n
end