Before splitting, you should choose the sizes of the smaller files. The standard size is what's normally fit on a standard floppy disk, but you may choose any size from a list of predefined sizes, by clicking at Base Size, see below. The most common removable media are listed there.
However, the list is fully editable. Both the names in the list and their related sizes in bytes, may be added, modified and removed by clicking at the Modify Base Sizes button (hidden by the drop down Base Size list in the figure above). In this case, a window like the one below pops up, where these changes may be entered. In this case, we have added the new base size with the description My Own Size with the related size of 700 000 000 bytes. This base size has entered the Base Size list up and been used in the list above.
You may also specify each individual smaller file's size, by clicking at the sizes and enter new values to the right, see below. The sizes below the changed one are modified if necessary by the program. Normally, the last size changes but also the number of smaller files might be modified.