import re


def is_number(string):
    """Test whether a string is numeric. Ignoring units like '$', 'cwt' and 'hd'."""

    string = re.sub(r'\$|[,-/]|cwt|he?a?d?', '', string, flags = re.IGNORECASE)
    try:
        float(string)
        return True
    except ValueError:
        return False