@staticmethod
def _quantity(quantity: [float, int]) ->float:
    """normalises quantity to a percentate float between 0 and 1.0"""
    if not isinstance(quantity, (int, float)) or not 0 <= quantity <= 100:
        return 1.0
    if quantity > 1:
        return round(quantity / 100, 2)
    return float(quantity)
