Bits 0-3 are used by the classroom-based command lists to indicate that or check whether a teacher has arrived at the classroom door to start the lesson.
Bit(s)
Meaning if set
0
Teacher has arrived at the Map Room
1
Teacher has arrived at the Reading Room
2
Teacher has arrived at the Exam Room
3
Teacher has arrived at the White Room
4-6
Unused
7
EINSTEIN is speaking (set by 7CAF; checked by 79BA and 7CC8; reset by 79CA)