def insulin_correction_units(from_value, to_value, effected_sensitivity):
    """ Computes a total insulin amount necessary to correct a glucose
        differential at a given sensitivity

    Arguments:
    from_value -- starting glucose value
    to_value -- desired glucose value
    effected_sensitivity -- sensitivity (mg/dL/U)

    Output:
    The insulin correction in units
    """
    if effected_sensitivity <= 0:
        return None
    glucose_correction = from_value - to_value
    return glucose_correction / effected_sensitivity
