def calculate_start_row_index(curr_page, nb_table_rows):
    """ Calculates row index of data that will be displayed given
        current page and number of rows in the table.

        Note:
            The first row of the table is reserved for displaying categories.

        Args:
            curr_page (int): current page number. Pages start from 1.
            nb_table_rows (int): number of rows in the table.

        Returns:
            int: data row index
    """
    if curr_page == 0:
        return 0
    return (curr_page - 1) * (nb_table_rows - 1)
