Period Letter Designations
The period letter is specified by the half-hour interval in which trading commences. The periods are as follows (time is Chicago time or US Central Standard time, i.e. GMT - 6 hours). In each case we label the periods by starting time, so that 0:00 represents the period running from midnight to one half-hour later in Chicago.
0:00 | i | 4:00 | r | 8:00 | A | 12:00 | I | 16:00 | R | 20:00 | a |
0:30 | j | 4:30 | s | 8:30 | B | 12:30 | J | 16:30 | S | 20:30 | b |
1:00 | k | 5:00 | t | 9:00 | C | 13:00 | K | 17:00 | T | 21:00 | c |
1:30 | l | 5:30 | v | 9:30 | D | 13:30 | L | 17:30 | V | 21:30 | d |
2:00 | m | 6:00 | w | 10:00 | E | 14:00 | M | 18:00 | W | 22:00 | e |
2:30 | n | 6:30 | x | 10:30 | F | 14:30 | N | 18:30 | X | 22:30 | f |
3:00 | p | 7:00 | y | 11:00 | G | 15:00 | P | 19:00 | Y | 23:00 | g |
3:30 | q | 7:30 | z | 11:30 | H | 15:30 | Q | 19:30 | Z | 23:30 | h |