Notes

• A suitable flat-field spectrum and arc spectrum should previously have been reduced and filed with the calibration system.

• Sky-object pairs may be observed in any sequence (for example sky-object-object-sky or object-sky-object-sky). Any observations with telescope offsets greater than 30 arcsec will be assumed to be a sky position. It is recommended that the observation types are set to OBJECT and SKY as appropriate (this is essential if your offsets to sky are smaller than 30 arcsec).

• Variances are propagated.

• Based on the spectroscopy recipe of the same name, and uses spectroscopy primitives.

• A datacube is formed of each subtracted pair and an image is extracted to allow you to confirm that your target is suitably located on the field, but no coadded datacube is formed.