• Move to a 12th mag star
• TV in continuous readout, viewing mobile probe
• SYS>af2 viewsky X Y (start with x/y = 0, then choose values such that the mobile probe views the rotator centre)
• USER>ROT SKY 'start_value' (e.g. start_value = 0)
• When in position measure x and y of the star
• Rotate 180 degrees, then measure x and y again
• Calculate the new rotator centre (see HERE for the most recent values)
• Mark the rotator centre and save the region file for future reference

• SYS> af2 viewsky X Y (using the values to view the rotator centre)
• USER> ROT MOUNT 'angle' (to stop the rotator moving and avoid problems with the rotator limits)
• USER> CAL FAINT
• TV in continuous readout, viewing mobile probe
• Centre up all stars on the rotator centre

Using a multi-object instrument it is recommended to define the aperture 0 offset, so the field rotates around the instrument centre. To do so a known good fiducial fibre should be placed on the instrument centre.

• USER> ROT FLOAT
• SYS> af2 viewsky X Y (same values as before)
• Centre a 12th mag star on the rotator centre (e.g. last pointing star)
• Move the mobile probe in steps of e.g. 300 to af2 viewsky 0 0 while maintaining the star on the rotator centre using HANDSET in APOFF mode
• Finally park the robot and centre the star on the fiducial fibre (if no fiducial fibre can be placed in the instrument centre skip this)
• USER> STORE AP 0
• Deploy the mobile probe again using af2 view sky 0 0. Mark the star position as the gripper centre (if no fiducial fibre can be placed in the instrument centre skip this)

Determining gripper centre:
Follow this to acquire a standard star on an AF2 science fibre, correcting for a possible offset between GRIPPER centre and MOBILE PROBE centre and also for a possible small displacement of the mobile-probe fibre at the AG CCD end. This assumes the sequence 'rot centre', 'calibrate' and 'define ap0' has been executed successfully. You must have a field setup (AFSETUP) ready and the rotator must track the demanded sky PA of the field.

• USER> gocat 'standard star'
• Now put the star under a fiducial fibre:
  
• SYS> af2 offsettel SKYPA STARNAME FIDUCIALFIBRENR
• Answer the questions (first 'no' then 'yes')
  
• Centre the star on the TV where you think the GRIPPER centre is
• SYS> af2 park (otherwise you won't see the star on the autoguider)
• Centre the star on the fiducial fibre on the TV
• SYS> af2 viewobject FIDUCIALFIBRENR (same fiducial fibre as above)
• See where the star ends up on the mobile probe CCD image
• Mark this position as the GRIPPER centre for future reference
• See HERE for the most recent values
• Now do the final step to put the star under a science fibre:
  
• SYS> af2 offsettel SKYPA STARNAME SCIENCEFIBRENR
• Answer the questions (first 'no' then 'yes')
• Centre the star (TV) on what you now know is the GRIPPER centre
• SYS> af2 park (or af2 sleep)

• To acquire move the robot to a fiducial object close to the instrument centre e.g.
  SYS > af2 viewobject 96
  and centre the star with the XY HANDSET on the GRIPPER centre
• Now move the mobile probe to another fiducial star at the edge of the field; this time move the rotator to centre the star as good as possible, then park the robot
  SYS > af2 sleep
  as now we proceed with the final tweak using the Autoguider.
• The last step is to tweak telescope and rotator to centre all guide fibres in use.
• Remember to set the telescope focus to the right value and to check/remark all fibre centres before as the fibre positions on the autoguider might change with EL!
• If you can't see the fiducial stars perform a spiral search, in this case it is recommended to redefine the GRIPPER centre on the mobile probe. Once found the best compromise start guiding.