The inability of some boxes to add new digital channels without a full re-scan—deleting all existing channel settings—renders them unusable to viewers who rely on directional antennas and rotors to receive distant stations. Signal strength meters, where available, are awkward, typically only displaying information for channels that have already been found. This is problematic, as digital signals are most often transmitted on higher frequencies or with far less power than their analog counterparts, requiring careful antenna installation, orientation and location to avoid obstructions, fading and multipath interference problems. Where the converter fails to receive a channel, an often-cumbersome manual process is usually provided; however, this requires knowledge of which frequencies each missing station is actually transmitting on, rather than the virtual channels each is mapped to by the ATSC protocol.