def version_update_scale(old_version_string, new_version_string):
    """"
    takes in version numbers old_version and new_version as strings, compares them, 
    and returns "major" "minor" or "micro" to indicate scale of update required to get to new.
    Returns None if the versions are the same
    
    major -> 1.x to 2.x
    minor -> 1.4 to 1.7
    micro ->  1.4.3 to 1.4.4
    """
    old_version = old_version_string.split('.')
    new_version = new_version_string.split('.')
    
    if old_version[0] != new_version[0]:
        return "major"
    elif old_version[1] != new_version[1]:
        return "minor"
    elif old_version == new_version:
        return None
    else:
        return "micro"