def convert_percentage_string_to_float(percentage_string):
    """Converts a string of the form 'xx.xx%' to its equivalent decimal value.

    :param percentage_string: A string in percentage form to be converted.
    :returns: A floating-point number rounded to 4 decimal places (2 decimals in percentage form).
    """
    return round(float(percentage_string.replace('%', '')) / 100, 4)