Letter  Periode Letter Periode
A  Jan. 1-15 N July 1-15
B Jan. 16-31 O July 16-31
C Feb. 1-15 P Aug. 1-15
D Feb. 16-29 Q Aug. 16-31
E Mar. 1-15 R Sept.1-15
F Mar. 16-31 S Sept.16-30
G Apr. 1-15 T Oct. 1-15
H Apr. 16-30 U Oct. 16-31
J May 1-15 V Nov. 1-15
K May 16-31 W Nov. 16-30
L  June 1-15 X Dec. 1-15
M June 16-30 Y Dec. 16-31

I wordt weggelaten en Z wordt niet gebruikt.

A = 1st F = 6th L = 11th Q = 16th V = 21st
B = 2nd G = 7th M = 12th R = 17th W = 22nd
C = 3rd H = 8th N = 13th S = 18th X = 23rd
D = 4th J = 9th O = 14th T = 19th Y = 24th
E = 5th K = 10th P = 15th U = 20th Z = 25th