Author: Ray Jones
The answer is Farenheit. If a person goes to lobby 7, sits at the
first coordinate on the floor grid, and looks at the second
coordinate, the letter in the inscription across the top in line with
their viewing vector is the next one in the sequence.
The clues for lobby 7: near the crossroads, "entertainment and
hacking"
The letters might be a little off the vector, ergo the "don't be too
exact".
The grid is (0,0) based.
The last line orients the grid (assuming a right-handed coordinate
system). There are post office mailboxes in the lobby in one corner.