This is the individual work centers you have in your shop, it is not every single machine you have in your shop.
Machines will be grouped into work centers. You can have up to 25 work centers and each work center can contain 10 machines. For example: Work center "A" can contain machine 1, machine 2, machine 3, machine 4, machine 5, machine 6, machine 7, machine 8, machine 9, and machine 10
One work center per line, no skipped lines. Alphanumeric characters only.