def get_units(filename: str, extension: str='.csv') ->tuple:
    """ Read the units from the raw signal file.

    :param filename: name of raw signal file, including path
    :param extension: extension of raw files (default '.csv')
    :rtype: tuple
    """
    with open(filename, 'r') as f:
        f.readline()
        u = f.readline()
        if extension == '.csv':
            units = u.replace('\n', '').split(',')
        else:
            units = u.replace('\r', '').split('\t')
    return units
