Single dish observations are explicitly differential: the signal from the On position (target+sky) is compared with the signal from the Off position (sky only). In position switching, the telescope points back and forth between the target and a nearby blank sky position.

1. Position switching with reference positions 300 arcsec (5 arcmin) away in azimuth.
   uip> oo_scan N /step 300 /altaz
   • The telescope will move symmetrically
     +OFF ON ON -OFF
   • N is the number of repetitions of this pattern.
   • Because the sky brightness does not change, moving in azimuth results in better subtraction.
2. Position switching with reference position chosen to avoid emission regions, etc.
   uip> oo_scan N /designated_off
   • The telescope will move asymmetrically
     OFF ON
   • N is the number of repetitions of this pattern.
   • The reference position must be specified in the source catalog as target:off_position.

There are other possibilities. For details, consult the online help,
uip> help oo_scan

• If the Secondary mirror is wobbling, it will be stopped before an oo scan, then restarted.