Note that the Master Map is an active map. From it, you can move to a sub-level by clicking on a "hot box." "Hot boxes" are those rectangles within the maps which are bold outlined. Notice, for example, the map reached by clicking on the box marked "Ear Mental Model" in the Master Map. The box labeled "Autograph Style" is outlined, while the box labeled "Ear Mental Model" is not. By clicking on the outlined box, you can move to a more detailed description of the information contained in the box. If you click on any portion of the map which is not active link, you will be returned to the table of contents page.
Some active maps also have "tunnels." These are live links to other maps in the project. These tunnels are meant to indicate a connection in Bell's thought processes which cannot be indicated in the general top-down structure of the master map. Tunnels are those pentagonal boxes in which a connection is described. In the example map described above, "From Manometric Flame" is a tunnel "from" the map page describing "The Manometric Flame Capsule or Flame Galvonometer Experiments." The box labeled "To Flame GalvonmeteExperiments" is a tunnel "to" the map page describing Bell's "Flame Galvonometer Experiments: February 24, 1876." Note that active tunnels are not bold-oultined, as are the other map links.