@misc{Tesar-Skala-Zdrahal-1987, 
    title={Patent: Power factor measuring equipment 
    (in {Czech}:  Zarizeni pro pro mereni uciniku)}, 
    author={Tesar, Rudolf and Skala, Vaclav and zdrahal, Karel}, 
    year={1987}, 
    month={May},
    country = {Czech Rep.},
    URL = {http://afrodita.zcu.cz/~skala/PUBL/PUBL\_1987/1987-patent-239283.pdf},
    note = {{Czech Rep.} Patent No.239283},
}