If the common block name is omitted, then blank common block is assumed.
Any common block name including blank common can appear more than once in COMMON statements in the same program unit. The list nlist following each successive appearance of the same common block name is treated as a continuation of the list for that common block name.
The size of a common block is the sum of the sizes of all the entities in the common block, plus space for alignment.
Within a program, all common blocks in different program units that have the same name must be of the same size. However, blank common blocks within a program are not required to be of the same size.