ZB - byte offset seeks.

zb: Sets a flag so that seek integers (returned by .TELL) take the form of a byte offset from the beginning of the file. If you do not specify this option, seek integers have two parts: the upper 14 bits represent the number of a block within the file and the lower 22 bits represent a character offset within that block.
For this option to work, the file format must be Media 4, with each record other than the last completely filling the block. The B and C libraries write Media 4 in this manner using the character handling functions, but other languages may create Media 4 files in different formats.