However, most ATSC tuners must re-scan for stations that change their RF channel. On some, this is as simple as manually punching in the new RF channel, at which point the decoder will read the PSIP data and re-map to the proper channel number. However, this may not delete the original mapping, leaving the original "dead" channels interleaved with the new ones (such as 5.1 old, 5.1 new, 5.2 old, 5.2 new), or possibly confusing the receiver (and the user). In many cases, a receiver will not automatically add the new mapping at all if an old one exists. Completely re-scanning will normally solve this, but may not pick up stations that are weak or temporarily off-air during the scan, causing the need to manually enter them (if this is even possible with the given receiver).
