#
# abbaper.pro
#
# Usage: call abbaper size1  nscans
#
# Take a abba seq of spectra perp to the slit offset by size1 arcsec. The 
# star should be centered along the slit. The telescope is returned to center
# after the sequence. Repeat the seq nscans times.
#
parameter size1 nscans

	if (size1==0.0)
	  ask 'What is the offset between spectra (arcsec)?' size1
	end_if

	if (nscans==0)
	  ask 'Number of sequences?' nscans
	end_if

 	call askpars
	
#
# this is the basic step (slit is EW, so offset is NS)
#
	stepn=size1
	stepn2=-2*size1
	stepe=0.0
 
	yorn 'Are the OBSERVE params OK and TELESCOPE centered'

        if (yorn~=1)
	  printf 'Aborting sequence: reset parameters/center telescope'
	  printf 'and try again'
	  return
        end_if

	yorn 'Disable the Tip Tilt guider during offsets'
        if (yorn==1)
          usetip=1
        else
          usetip=2
        end_if

#
# begin sequence
#
	do j=1,nscans

#
# position a
#
	  avego $coad
	
#
# position b1
#
	  if (usetip==1)
            call ttd
          end_if
          offset ra=stepe dec=stepn 
          if (usetip==1)
            call tte
          end_if
	  avego $coad
#
# position b2
#
          if (usetip==1)
            call ttd
          end_if
          offset ra=stepe dec=stepn2
          if (usetip==1)
            call tte
          end_if
          avego $coad
#
# position a
#

	  if (usetip==1)
            call ttd
          end_if
          offset ra=stepe dec=stepn
          if (usetip==1)
            call tte
          end_if
          avego $coad
	
	end_do

	alert 'SCAN COMPLETED' 3 1

return