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> oo_scan N /step 300 /altaz
+OFF ON ON -OFF
uip> oo_scan N /designated_off
There are other possibilities. For details, consult the online help,
uip> help oo_scan
ooscan, then restarted.