def unit_to_factor_in_microns(unit: str) ->float:
    """
        Convert a string naming the unit of measure to its value in microns
        :param unit:
        :return:
        """
    if unit == 'microns':
        return 1.0
    if unit == 'millimeters':
        return 1000.0
    if unit == 'centimeters:':
        return 10000.0
    if unit == 'meters':
        return 1000000.0
