After the late night shows, programming varies; this time slot between approximately 2:00 and 6:00 a.m. is known as overnight (or the "graveyard slot" due to the extremely low numbers of viewers). This daypart is the only portion of the day not monitored or reported on by Nielsen in the U.S. in most circumstances, although many stations still consider this a viable programming daypart and actively sell breaks. Some stations may sign-on and sign-off for the night (though this has become less common since the 1980s), air infomercial, or air news or reruns of other programming. It is also often used as a timeslot to "burn off" (air programming the station is required to run) shows the station is contractually obligated to run but is not concerned with viewership, often after an announced cancellation or poor ratings performance. This daypart can also be used to air programming intended to be recorded via DVR and watched later ("time shifting"), or a spot to air programming preempted from another daypart due to breaking news, live sports, or other program interruptions. Many stations run rebroadcasts of local late news broadcasts at 2:00 a.m., with visual disclaimers that indicate the programming is pre-recorded. In many areas, PBS member stations may also air encores of children's programs on a digital subchannel at this time.