The machine contains the mechanical equipment that was needed to operate switches which controlled the track sections that lies just east of the building. On the surface of the board is a representation of track sections in the Harrisburg yard that were controlled from the building. The board also incorporates colored lights that indicate the status of signals and switches as well as occupancy of different tracks by trains. The track representation on the board has been revised to reflect modifications of the railroad's track layout. To the east of the interlocking machine is a long wooden desk.
Communications equipment is mounted on the desk, some original and some more modern.
The front of the desk faces the machine, and behind the desk is the projecting bay, which is composed of three windows on its east elevation, and on its north and south sides. The bay projects about four feet from the building and affords an easy view along the tracks in all directions. Listing Harris Tower on the National Register of Historic Places will better recognize this industrial gem, and help open funding opportunities for conservation and interpretation of the Tower. If approved, the Bureau for Historic Preservation will submit the nomination to the National Park Service for listing on the National Register of Historic Places. Penndustry is the biannual newsletter of the Pennsylvania Historical and Museum Commission's Industrial Survey of Pennsylvania.