The following table text for the principle number 9 shows how multiplication was done in the sexagesimal, or base 60, number system.

Obverse

1	9
2	18
3	27
4	36
5	45
6	54
7	1,3	(=63)
8	1,12	(=72)
9	1,21	(=81)
10	1,30	(=90)
11	1,39	(=99)
12	1,48	(= 108)
13	1,57	(= 117)
14	2,6	(= 126)

On the front (obverse) and the back (reverse) of this Old Babylonian school tablet, cuneiform signs are written in two columns. In the left-hand column of the obverse are the signs for 1 through 14, and on the reverse, 15 through 19 (here written "20 minus 1" instead of the more usual "10 plus 9"), then 20, 30, 40, 50, and 500. In the righthand column (beginning on the obverse and continuing on the reverse) are the numbers 9, 18, 27, 36, 45, 54, 63, and so on, each 9 times the number opposite it in the left-hand column. In order to get 63, for example, the vertical wedge and the three that follow must be read 1,3 or 1.60 + 3 = 63. The following lines would be 1,12 = 72; 1,21 = 81; and so on.

Reverse

15	2,15	(= 135)
16	2,24	(= 144)
17	2,33	(= 153)
18	2,42	(= 162)
19	2,51	(= 171)
20	3	(= 180)
30	4,30	(= 270)
40	6	(= 360)
50	7,30	(= 450)
8,20 a.ra 1	8,20	(= 500)

In the fourteenth line, the two...