====== Position Switching ======

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.

==== UIP commands ====

  - 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.
  - 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 [[cso:telescope:uip:catalog|catalog]] as //target//:off_position.

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

==== Caveats ====

  * If the [[cso:telescope:secondary]] is wobbling, it will be stopped before an ''oo'' scan, then restarted.