def get_product_from_time_scale(time_scale):
    """
    get the the USGS nwis product that is appropriate for the time scale
    :param time_scale: str - Pandas like time string for the time scale at which
    the data will be aggregated (e.g., 'H' for hour or 'D' for daily)
    :return:
    """
    iv_scales = ['15T', 'T', 'H']
    dv_scale = ['D']
    if time_scale in iv_scales:
        return 'iv'
    elif time_scale in dv_scale:
        return 'dv'
    else:
        raise ValueError("time scale must be '15T', 'T', 'H', or 'D'")