; FQTOL
;---------------------------------------------------------------
;! Frequency tolerance with which FQ or frequency entries are accepted.
;# ADVERB CALIBRATION
;-----------------------------------------------------------------------
;;  Copyright (C) 1995, 2020
;;  Associated Universities, Inc. Washington DC, USA.
;;
;;  This program is free software; you can redistribute it and/or
;;  modify it under the terms of the GNU General Public License as
;;  published by the Free Software Foundation; either version 2 of
;;  the License, or (at your option) any later version.
;;
;;  This program is distributed in the hope that it will be useful,
;;  but WITHOUT ANY WARRANTY; without even the implied warranty of
;;  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
;;  GNU General Public License for more details.
;;
;;  You should have received a copy of the GNU General Public
;;  License along with this program; if not, write to the Free
;;  Software Foundation, Inc., 675 Massachusetts Ave, Cambridge,
;;  MA 02139, USA.
;;
;;  Correspondence concerning AIPS should be addressed as follows:
;;         Internet email: aipsmail@nrao.edu.
;;         Postal address: AIPS Project Office
;;                         National Radio Astronomy Observatory
;;                         520 Edgemont Road
;;                         Charlottesville, VA 22903-2475 USA
;-----------------------------------------------------------------------
;---------------------------------------------------------------
FQTOL     LLLLLLLLLLLLUUUUUUUUUUUU CCCCCCCCCCCCCCCCCCCCCCCCCCCCC
----------------------------------------------------------------
FQTOL
Type: Adverb  (Scalar)
Use:  Standard data selection adverb, used to define a frequency
      tolerance within which data with different frequencies
      are assigned the same FQ number. Is mainly used when
      merging uv data files together.
      Example: if file A has freq #1 and file B has freq #2
      then they will be given the same FQ number if
        (freq #1 + FQTOL) < freq #2 > (freq #1 + FQTOL).
Null Value:  -1
      A null value means set FQTOL to be the maximum frequency
      difference a source can have in one day, i.e.
          FQTOL = ref. freq * (30 km/s) / (30000 km/s)
Tasks:
   DBAPP.......Appends one or more data sets to the output data set.
               FQTOL is the tolerance in kHz to not renumber FQs.
   DBCON.......Concatenates two UV data sets.  FQTOL is the tolerance in
               kHz to not renumber FQs.
   FITLD.......Reads FITS files to load images or UV (IDI or UVFITS)
               data to disk.
   FXPOL.......Corrects VLBA polarization assignments.  FQTOL is
               tolerance in kHz for matching IFs.
   IMAGR.......Wide-field and/or wide-frequency Cleaning / imaging
               task.  FQTOL sets the range of frequencies which get the
               same frequency-dependent beam and model.
   OOSUB.......Subtracts/divides a model from/into a uv data base.
               FQTOL sets the range of frequencies which get the same
               frequency-dependent beam and model.
   OTFBS.......Translates on-the-fly continuum SDD format to AIPS UV
               file.  FQTOL in MHz tolerance to concatenate files.
   OTFUV.......Translates on-the-fly single-dish SDD format to AIPS UV
               file.  FQTOL in MHz tolerance to concatenate files.
   PCLOD.......Reads ascii file containing pulse-cal info to PC table.
               FQTOL in kHz is tolerance in IF match for pre-DiFX data.
   VLOG........Pre-process external VLBA calibration files.  FQTOL is
               the tolerance in kHz for matching IF frequencies.
Procedures:
   IMFRING.....Large image delay fitting with IM2CC and OOFRING.
               FQTOL is passed to OOSUB.
   IMSCAL......Large image self-cal with IM2CC and OOCAL.
               FQTOL is passed to OOSUB.
   LINIMAGE....Build image cube from multi-IF data set.
               FQTOL is passed to IMAGR.
   OOCAL.......Determines antenna complex gain with frequency-dependent
               models.  FQTOL is passed to OOSUB.
   OOFRING.....Fringe fit data to determine calibration with spectral
               index options.  FQTOL is passed to OOSUB.
----------------------------------------------------------------