Proposers may apply to use any of the pre-defined instrument observing modes described in the Observers' manuals. These pre-defined observing modes or 'Astronomical Observation Templates' (AOTs) are made available through HSpot. Once an AOT has been chosen, the detailed observing parameters for that particular observing mode need to be entered using HSpot resulting in an 'Astronomical Observation Request' (AOR). AORs are the primary units of Herschel observing time.