The BLKOFF option controls whether the offsets shown in the pseudo-assembler listing (produced by the LIST option) and the statement offset listing (produced by the OFFSET option) are from the start of the current module or from the start of the current procedure.
.-BLKOFF---. >>-+-NOBLKOFF-+------------------------------------------------><
The pseudo-assembler listing also includes the offset of each block from the start of the current module (so that the offsets shown for each statement can be translated to either block or module offsets).