I = 1
V = 5
X = 10
L = 50
C = 100
D = 500
M = 1,000
The roman numerals are multiplied by a thousand when a line is drawn over the figure, and by one million when two lines are drawn over the figure.
M = 1,000,000
No figure of a roman numeral can be repeated more than three times in succession.
III = 3 XXX = 30 CCC = 300
In roman numerals the letters V, L and D can not be duplicated because twice the values of each can be represented by: X, C and M.
If a figure is placed to the right of another with a value less than or equal to it, the values are added together.
VII = 7 XX = 20 CLXVIII = 168
If a lower figure is placed to the left of another, the value is subtracted from the larger figure to the right.
IV = 4 IX = 9 XL = 40
