public function getSByte($offset = 0)
    {
        /*
         * Validate the offset --- this throws an exception if offset is
         * out of range.
         */
        $this->validateOffset($offset);

        /* Translate the offset into an offset into the data. */
        $offset += $this->start;

        /* Return a signed byte. */
        return PelConvert::bytesToSByte($this->data, $offset);
    }