'format example: m Kg^2 / s^2'

@staticmethod
def parsed_from(unit_string, positive=None):

    if (positive is None):
        positive = True
        for delta_string in Units.delta_strings:
            if unit_string.startswith(delta_string):
                unit_string = unit_string[len(delta_string):]
                positive = False
                break
    dimensions = {}
    for (factor, dimension_counts) in zip((1, (-1)), unit_string.split('/')):
        for match in counted_dimension_pattern.finditer(dimension_counts):
            dimension_spec = match.group()
            if ('^' in dimension_spec):
                (dimension, count) = dimension_spec.split('^')
            else:
                dimension = dimension_spec
                count = 1
            count = (factor * int(count))
            try:
                existing_count = dimensions[dimension]
            except KeyError:
                dimensions[dimension] = count
            else:
                dimensions[dimension] += count
    return Units(dimensions, positive)
