def _get_metric_prefix(power: int, default: str = "") -> str:
    """Return the metric prefix for the power.

    Args:
        power (int): The power whose metric prefix will be returned.
        default (str): The default value to return if an exact match is
            not found.

    Returns:
        str: The metric prefix.
    """
    metric_prefix = {
        24: "Y",
        21: "Z",
        18: "E",
        15: "P",
        12: "T",
        9: "G",
        6: "M",
        3: "k",
        -3: "m",
        -6: "μ",
        -9: "n",
        -12: "p",
        -15: "f",
        -18: "a",
        -21: "z",
        -24: "y",
    }
    return metric_prefix.get(power, default)