def deltanpq(phino, phinoopt=0.2):
    """Calculate deltaNPQ

    deltaNPQ = (1/phinoopt) - (1/phino)

    :param phino: PhiNO
    :param phinoopt: Optimum PhiNO (default: 0.2)
    :returns: deltaNPQ (float)
    """
    return (1/phinoopt) - (1/phino)