Compare the short- and long-period variants of the DI Mendeleev’s table.

Similarity: periods and groups are distinguished in the structure of both tables. There are 7 periods. The main subgroups are designated by the letter A, and the secondary ones are indicated by B.
Difference: in the short-period version, the system has rows, and in the long-period version, they are absent. Therefore, in the short-period version of the table, there are 8 groups, which are numbered with Roman numerals from I to VIII, and in the long-period – 18, which denote either Arabic numerals or Roman numerals indicating the A- or B-group, similar to the short-period version. In the short-period version of the table, the main and secondary subgroups are also distinguished by the placement of the element (to the left or right of the center of the cell).