from typing import Tuple


def _get_start_size(d: dict) -> Tuple[int, int]:
    """Returns a tuple of ints that represent the true start byte and size
    based on the provided dict.

    This is a convenience function such that if you have these values in a
    dictionary with a *StartByte* and *Bytes* keys.

    Since the StartByte labels on an ISIS cube are 1-based counts, and not
    0-based, in order to convert from the numbers provided in the labels
    to a byte count for Python's read() functions, you must subtract one
    from the listed StartByte, which this function does.
    """
    start = int(d["StartByte"]) - 1
    size = int(d["Bytes"])
    return start, size