To be more specific:

The `offset` argument to *numpy.memmap* gets (more or less directly) passed to Python's *mmap.mmap*. In the *mmap* docstring, it says

> offset may be specified as a non-negative integer offset. mmap references will be relative to the offset from the beginning of the file. offset defaults to 0. offset must be a multiple of the ALLOCATIONGRANULARITY.