This code combines Roman and Arabic numerals. Each letter of the alphabet has an Arabic numeral or Roman numeral assigned to it. Roman numerals are more complicated to write than Arabic numerals. No number should be longer than 2 characters. If you can write a number with two or fewer Roman numerals, a Roman numeral is used. If it takes three characters to write a number, an Arabic number is used. See the chart below.
I
II
3
IV
V
VI
7
8
IX
X
XI
12
13
A
B
C
D
E
F
G
H
I
J
K
L
M
14
XV
16
17
18
19
XX
21
22
23
24
25
26
N
O
P
Q
R
S
T
U
V
W
X
Y
Z
13 XV 14 V 25 / IV XV V 19 ‘ XX / 7 18 XV 23 / XV 14 / XX 18 V V 19.